test: add ping res log

pkg/mqtt/connection.go

@@ -278,6 +278,7 @@ func (c *Connection) RcvMsgFromClient() {
 
 		case *PingReq:
 			pingrsp := &PingResp{}
+			server.Log.Infof("%s, comes ping res", c.DeviceCode)
 			err := c.Mgr.Provider.OnDeviceHeartBeat(c.DeviceCode)
 			if err != nil {
 				server.Log.Errorf("%s, heartbeat set error %s, close now...", host, err)