REP-323 Make API Coverage in API Validator Configurable

I'm not really happy with the unit test, but using reflection makes it worse. Polymorphism is tested for handlers (instanceof), and a counter keeps track of the number of InstrumentedHandlers were added (should be 1 for the validator with the flag set and 0 for the other validator).
A few more alternatives:
cover-api-state
api-path-coverage
enable-path-coverage
api-stuff-state-things-coverage-go