Test that we deal with ServerCrashProcedure zero'ing out the targetServer in the
RegionStateNode in the midst of our doing an assign. The trickery is done above in
TargetServerBeingNulledOnUsAssignProcedure. We skip a bunch of logic to get at the guts
where the problem happens (We also skip-out the failure handling because it'd take a bunch
of mocking to get it to run). Fix is inside in RemoteProcedureDispatch#addOperationToNode.
It now notices empty targetServer and just returns false so we fall into failure processing
and we'll reassign elsewhere instead of NPE'ing. The fake of ServerCrashProcedure nulling out
the targetServer happens inside in updateTransition just after it was called but before it
gets to the near the end when addToRemoteDispatcher is called. See the
TargetServerBeingNulledOnUsAssignProcedure class above. See HBASE-19218.
Before fix, this test would fail w/ a NullPointerException.