public static RpcClient createClient(Configuration conf, String clusterId,
    MetricsConnection metrics) {
    return createClient(conf, clusterId, null, metrics, Collections.emptyMap());
  }
Creates a new RpcClient by the class defined in the configuration or falls back to
RpcClientImpl
@param conf      configuration
@param clusterId the cluster id
@param metrics   the connection metrics
@return newly created RpcClient
hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/RpcClientFactory.java