Perform a semi-graceful shutdown of the Drill-on-YARN AM. We send a message
to the AM to request shutdown because the YARN-provided message just kills
the AM. (There seems to be no way to get YARN to call its own
AMRMClientAsync.CallbackHandler.onShutdownRequest message.) The AM, however,
cannot gracefully shut down the drill-bits because Drill itself has no
graceful shutdown. But, at least this technique gives the AM a fighting
chance to do graceful shutdown in the future.
Fields inherited from class org.apache.drill.yarn.client.ClientCommand