Reopen region while server crash can cause the procedure to be stuck

Found this when implementing HBASE-20424, where we will transit the peer sync replication state while there is server crash.

The problem is that, in ServerCrashAssign, we do not have the region lock, so it is possible that after we call handleRIT to clear the existing assign/unassign procedures related to this rs, and before we schedule the assign procedures, it is possible that that we schedule a unassign procedure for a region on the crashed rs. This procedure will not receive the ServerCrashException, instead, in addToRemoteDispatcher, it will find that it can not dispatch the remote call and then a FailedRemoteDispatchException will be raised. But we do not treat this exception the same with ServerCrashException, instead, we will try to expire the rs. Obviously the rs has already been marked as expired, so this is almost a no-op. Then the procedure will be stuck there for ever.

A possible way to fix it is to treat FailedRemoteDispatchException the same with ServerCrashException, as it will be created in addToRemoteDispatcher only, and the only reason we can not dispatch a remote call is that the rs has already been dead. The nodeMap is a ConcurrentMap so I think we could use it as a guard.