Adding a /healthz url to vttablet.

It reflects the last result of the health check.
Adding integration tests to confirm it's wired up properly.
Adding a health check for query service in the right state.

CHanging the health check interface to pass a flag indicating
if QS should be running or not.
Now checking tabletserver.IsHealthy in health check.
Fixing health links in vttablet status page.
Changing ok message for health check.
Minor updates to Java tests

- Remove println in MapReduceIT
- Mark integrityexception test as ignored
Travis and Coveralls integration

Add travis configuration and dependencies script
Split integration test make targets to allow parallel execution in Travis
Add go packages required for coverage upload to Coveralls
Add coveralls and travis badges to README

Travis: Retry make targets to address flaky targets