MB-70173: Don't use static storage for MockConnection's description

This is the problematic code:

  const T& MockConnection::getDescription() const {
      static T obj{..};
      return obj;
  }

Problem with that is that in ep_testsuite that memory is (1) allocated
the first time the function is called (which is in a Bucket context)
and (2) then released when the program shuts down (ie outside Bucket
context, as at that point any bucket instance as been already released).

In local testing that shows up like

% env CB_ARENA_MALLOC_VERIFY_DEALLOC_CLIENT=1 lldb -- ../source_morpheus/build/kv_engine/ep_testsuite_dcp "-v" "-e" "compression_mode=active;item_eviction_policy=full_eviction;dbname=./ep_testsuite_dcp.full_eviction.comp_active.db" -C 90
(lldb) pr la
Process 11613 launched: '../source_morpheus/build/kv_engine/ep_testsuite_dcp' (arm64)
Running [90/91]: test oso backfill...(125 ms) OK
===ERROR===: JeArenaMalloc deallocation mismatch
	Memory freed by client:100 domain:None which is assigned arena:0, but memory was previously allocated from arena:2 (client-specific arena).
	Allocation address:0x1047fe4a0 size:24
..
Process 11613 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGABRT
    frame #0: 0x00000001816955f0 libsystem_kernel.dylib` __pthread_kill  + 8
libsystem_kernel.dylib`:
->  0x1816955f0 <+8>:  b.lo   0x181695610               ; <+40>
    0x1816955f4 <+12>: pacibsp
    0x1816955f8 <+16>: stp    x29, x30, [sp, #-0x10]!
    0x1816955fc <+20>: mov    x29, sp
Target 0: (ep_testsuite_dcp) stopped.
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGABRT
  * frame #0: 0x00000001816955f0 libsystem_kernel.dylib` __pthread_kill  + 8
    frame #1: 0x00000001816cdc20 libsystem_pthread.dylib` pthread_kill  + 288
    frame #2: 0x00000001815daa30 libsystem_c.dylib` abort  + 180
    frame #3: 0x0000000100fb71a8 ep_testsuite_dcp` cb::verifyMemDeallocatedByCorrectClient(client=0x000000016fdfeca8, ptr=0x00000001047fe4a0, size=24)  + 536 at je_arena_malloc.cc:260
    frame #4: 0x0000000100fb7238 ep_testsuite_dcp` cb::_JEArenaMalloc<cb::JEArenaSimpleTracker>::sized_free(ptr=0x00000001047fe4a0, size=24)  + 84 at je_arena_malloc.cc:455
    frame #5: 0x00000001000e29f4 ep_testsuite_dcp` cb::_ArenaMalloc<cb::_JEArenaMalloc<cb::JEArenaSimpleTracker>>::sized_free(ptr=0x00000001047fe4a0, size=24)  + 32 at cb_arena_malloc.h:273
    frame #6: 0x00000001000e29c0 ep_testsuite_dcp` cb_sized_free(ptr=0x00000001047fe4a0, size=24)  + 44 at cb_malloc_arena.cc:75
    frame #7: 0x00000001000e2fcc ep_testsuite_dcp` operator delete(ptr=0x00000001047fe4a0, size=24)  + 32 at global_new_replacement.cc:146
    frame #8: 0x0000000100030a24 ep_testsuite_dcp` void std::__1::__libcpp_operator_delete[abi:ue170006]<void*, unsigned long>(__args=0x00000001047fe4a0, __args=24)  + 32 at new:308
    frame #9: 0x00000001000309c4 ep_testsuite_dcp` void std::__1::__do_deallocate_handle_size[abi:ue170006]<>(__ptr=0x00000001047fe4a0, __size=24)  + 32 at new:334
    frame #10: 0x0000000100030960 ep_testsuite_dcp` std::__1::__libcpp_deallocate[abi:ue170006](__ptr=0x00000001047fe4a0, __size=24, __align=8)  + 80 at new:348
    frame #11: 0x00000001000676b4 ep_testsuite_dcp` std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>::deallocate[abi:ue170006](this=0x000000016fdfee85, __p="me", __n=1)  + 48 at allocator.h:130
    frame #12: 0x0000000100067678 ep_testsuite_dcp` std::__1::allocator_traits<std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>>::deallocate[abi:ue170006](__a=0x000000016fdfee85, __p="me", __n=1)  + 40 at allocator_traits.h:288
    frame #13: 0x000000010007c964 ep_testsuite_dcp` nlohmann::json_abi_v3_11_3::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::json_abi_v3_11_3::adl_serializer, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>>, void>::json_value::destroy(this=0x000000016fdff0c0, t=string)  + 1212 at json.hpp:646
    frame #14: 0x000000010007c490 ep_testsuite_dcp` nlohmann::json_abi_v3_11_3::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::json_abi_v3_11_3::adl_serializer, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>>, void>::data::~data(this=0x000000016fdff0b8)  + 36 at json.hpp:4225
    frame #15: 0x0000000100077fb8 ep_testsuite_dcp` nlohmann::json_abi_v3_11_3::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::json_abi_v3_11_3::adl_serializer, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>>, void>::data::~data(this=0x000000016fdff0b8)  + 28 at json.hpp:4224
    frame #16: 0x0000000100085e58 ep_testsuite_dcp` nlohmann::json_abi_v3_11_3::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::json_abi_v3_11_3::adl_serializer, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>>, void>::~basic_json(this=0x000000016fdff0b8)  + 44 at json.hpp:1266
    frame #17: 0x0000000100064694 ep_testsuite_dcp` nlohmann::json_abi_v3_11_3::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::json_abi_v3_11_3::adl_serializer, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>>, void>::~basic_json(this=0x000000016fdff0b8)  + 28 at json.hpp:1264
    frame #18: 0x000000010007c874 ep_testsuite_dcp` nlohmann::json_abi_v3_11_3::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::json_abi_v3_11_3::adl_serializer, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>>, void>::json_value::destroy(this=0x0000000101500b80, t=object)  + 972 at json.hpp:621
    frame #19: 0x000000010007c490 ep_testsuite_dcp` nlohmann::json_abi_v3_11_3::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::json_abi_v3_11_3::adl_serializer, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>>, void>::data::~data(this=0x0000000101500b78)  + 36 at json.hpp:4225
    frame #20: 0x0000000100077fb8 ep_testsuite_dcp` nlohmann::json_abi_v3_11_3::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::json_abi_v3_11_3::adl_serializer, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>>, void>::data::~data(this=0x0000000101500b78)  + 28 at json.hpp:4224
    frame #21: 0x0000000100085e58 ep_testsuite_dcp` nlohmann::json_abi_v3_11_3::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::json_abi_v3_11_3::adl_serializer, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>>, void>::~basic_json(this=0x0000000101500b78)  + 44 at json.hpp:1266
    frame #22: 0x0000000100064694 ep_testsuite_dcp` nlohmann::json_abi_v3_11_3::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::json_abi_v3_11_3::adl_serializer, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>>, void>::~basic_json(this=0x0000000101500b78)  + 28 at json.hpp:1264
    frame #23: 0x000000018158b2e8 libsystem_c.dylib` __cxa_finalize_ranges  + 476
    frame #24: 0x000000018158b070 libsystem_c.dylib` exit  + 44
    frame #25: 0x00000001816e6850 libdyld.dylib` dyld4::LibSystemHelpers::exit(int) const  + 20
    frame #26: 0x00000001813431a0 dyld` start  + 2552

Change-Id: I6e4b8203eb5dfd67352386895d87dfd52f6c6641
Reviewed-on: https://review.couchbase.org/c/kv_engine/+/238640
Tested-by: Build Bot <build@couchbase.com>
Reviewed-by: Paolo Cocchi <paolo.cocchi@couchbase.com>
Well-Formed: Restriction Checker
Reviewed-by: Mohammad Zaeem <mohammad.zaeem@couchbase.com>

Author: paolococchi

programs/engine_testapp/mock_cookie.cc

@@ -26,7 +26,6 @@ void MockConnection::setUserScheduleDcpStep(std::function<void()> func) {
     userScheduleDcpStep = std::move(func);
 }
 const nlohmann::json& MockConnection::getDescription() const {
-    static nlohmann::json description{{"peer", "you"}, {"socket", "me"}};
     return description;
 }
 const cb::rbac::UserIdent& MockConnection::getUser() const {

programs/engine_testapp/mock_cookie.h

@@ -53,6 +53,7 @@ class MockConnection : public ConnectionIface {
 protected:
     ConnectionPriority priority{ConnectionPriority::Medium};
     cb::rbac::UserIdent user{"nobody", cb::rbac::Domain::Local};
+    const nlohmann::json description{{"peer", "you"}, {"socket", "me"}};
 };
 
 class MockCookie : public CookieIface {