RemoteClusterSerice could update metakv but fail to update local cache

1) For Add/Set/Del functions in RemoteClusterService.   It could update metakv but fail to update the cache.   Once metakv is updated, it will propagate the change across the cluster.  

2) When the remote cluster service is updated in metakv, it will receive a metakv change notification.   This will, in turn, call remoteClusterChangeHandlerCallback().   Later, when the reference is update in the local cach, it will explicitly call remoteClusterChangeHandlerCallback() for the second time.  It is not clear why it has to be called twice.