Adding a RPC command to run health check on a tablet.

Using it in tests to make sure it doesn't alter the serving state
of a tablet.
Merge branch 'master' into replication
Java client: Add IntegrityException
Merge pull request #124 from youtube/replication

Replication
Merge pull request #127 from youtube/vitess-java

Java client: Add IntegrityException
Merge branch 'master' into resharding