Enable adb -H adbSrvIp -P adbSrvPort furthermore
   because port forward is done in ADB server side, so jsonRpc request should be sent to ADB server:
       http://localhost:%d/jsonrpc/   changed to = > http://172.21.137.5:%d/jsonrpc/

 Add debug log
 Redirect log of jsonRpcServer to /data/local/tmp/uiautomator.log