Replication fails to delete all corresponding zk nodes when peer is removed

When removing a peer, the client side will delete peerId under peersZNode node; then alive region servers will be notified and delete corresponding hlog queues under its rsZNode of replication. However, if there are failed servers whose hlog queues have not been transferred by alive servers(this likely happens if setting a big value to "replication.sleep.before.failover" and lots of region servers restarted), these hlog queues won't be deleted after the peer is removed. I think remove_peer should guarantee all corresponding zk nodes have been removed after it completes; otherwise, if we create a new peer with the same peerId with the removed one, there might be unexpected data to be replicated.