Implement a general framework to execute remote procedure on RS

When building the basic framework for HBASE-19064, I found that the enable/disable peer is built upon the watcher of zk.

The problem of using watcher is that, you do not know the exact time when all RSes in the cluster have done the change, it is a 'eventually done'.

And for synchronous replication, when changing the state of a replication peer, we need to know the exact time as we can only enable read/write after that time. So I think we'd better use procedure to do this. Change the flag on zk, and then execute a procedure on all RSes to reload the flag from zk.

Another benefit is that, after the change, zk will be mainly used as a storage, so it will be easy to implement another replication peer storage to replace zk so that we can reduce the dependency on zk.