@After
  public void tearDown() throws Exception {
    Closeables.close(client, true);
    server.stop();
    group.shutdownGracefully().sync();
  }
Confirm that we truly close the NettyRpcConnection when the netty channel is closed.
hbase-server/src/test/java/org/apache/hadoop/hbase/ipc/TestNettyIPCCloseConnection.java