Broken RemoteInterpreterService.Client is reused, not discarded

Looking into the Zeppelin code, there're getClient() and releaseClient() in RemoteInterpreterProcess, but RemoteInterpreterProcess doesn't expose releaseBrokenClient() which discards broken client from pool.

This means Zeppelin always return Client to pool whether it is broken or not, so broken Client instances are reused or even leaked if releaseClient() is not called.