Allow running only a single scenario or feature file

[ms14981]

Currently, npm test runs all features. Work out how to run a subset, and document!

We call mvn test through Node so we will need to change startTests.js to pass through command line arguments.
https://stackoverflow.com/questions/34772622/how-to-run-single-cucumber-feature-files-through-command-prompt-and-through-jenk