Make enableReplicationPeer/disableReplicationPeer idempotent

When enableReplicationPeer is called and the peer is already enabled, DoNotRetryIOException is being thrown as part of preEnablePeer here, similarly with disableReplicationPeer here.

java.lang.RuntimeException: org.apache.hadoop.hbase.DoNotRetryIOException: Replication peer 1 has already been enabled

Ideally, it should not throw a runtimeException, if the peer is already in desired state

Either 1. we should add a check before trying to enable/disable peer, and if it is already enabled return, else enable the peer or
2. Log the message instead of throwing exception in preEnablePeer/preDisablePeer