Start app by bundle_id
        Args:
            - bundle_id(string): ex com.netease.my
        Returns:
            idevicedebug subprocess instance

def start_app(self, bundle_id):
        '''
        Start app by bundle_id
        Args:
            - bundle_id(string): ex com.netease.my
        Returns:
            idevicedebug subprocess instance
        '''
        idevicedebug = must_look_exec('idevicedebug')

        # run in background
        kwargs = {'stdout': subprocess.PIPE, 'stderr': subprocess.PIPE}
        if sys.platform != 'darwin':
            kwargs['close_fds'] = True
        return subprocess.Popen([idevicedebug, "--udid", self.udid, 'run', bundle_id], **kwargs)