@Override
      public void run() {
        cleanupIdleConnections();
      }
Construct an IPC client for the cluster <code>clusterId</code>
@param conf      configuration
@param clusterId the cluster id
@param localAddr client socket bind address.
@param metrics   the connection metrics
hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/AbstractRpcClient.java