enter arbitrary mode

def set_mode_apm(self, mode, custom_mode = 0, custom_sub_mode = 0):
        '''enter arbitrary mode'''
        if isinstance(mode, str):
            mode_map = self.mode_mapping()
            if mode_map is None or mode not in mode_map:
                print("Unknown mode '%s'" % mode)
                return
            mode = mode_map[mode]
        # set mode by integer mode number for ArduPilot
        self.mav.set_mode_send(self.target_system,
                               mavlink.MAV_MODE_FLAG_CUSTOM_MODE_ENABLED,
                               mode)