examples/15_muti_robot/multi_drone/01_scan_ip.py will be stuck when there are not enough drones

[tianb03]

The function will be stuck, though function multi_drone._get_sn(timeout) takes in 10 sec timeout. However, multi_drone.initialize(num=drone_num) is trying to get enough drones in the sub net.

in tool.py line 234, in TelloConnection. _scan_host function

        while len(self._robot_host_list) < num:
            logger.info('[Still_Searching]Trying to find Tello in subnets...\n')

May I know if it is designed in purpose or may be a bug? Thx in advance.