private synchronized ServerName createRegionServerStatusStub() {
    // Create RS stub without refreshing the master node from ZK, use cached data
    return createRegionServerStatusStub(false);
  }
Get the current master from ZooKeeper and open the RPC connection to it. To get a fresh
connection, the current rssStub must be null. Method will block until a master is available.
You can break from this block by requesting the server stop.
@return master + port, or null if server has been stopped
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java