DRILL-5723: Added System Internal Options That can be Modified at Runtime
Changes include:
1. Addition of internal options.
2. Refactoring of OptionManagers and OptionValidators.
3. Fixed ambiguity in the meaning of an option type, and changed its name to accessibleScopes.
4. Updated javadocs in the Option System classes.
5. Added RestClientFixture for testing the Rest API.
6. Fixed flakey test in TestExceptionInjection caused by race condition.
7. Fixed various tests which started zookeeper but failed to shut it down at the end of tests.
8. Added port hunting to the Drill Webserver for testing
9. Fixed various flaky tests
10. Fix compile issue
closes #923
