kill_cmds is list of DockerCmd/BgCommand/other_class_with_execute(). Anyway sometimes I don't want to use DockerCmd, but kill the process directly with `os.kill()`. In such case I set kill_command to False, which is special value reserved for such situation. The main process knows, that it shouldn't execute False, but look for the current expected signal and kill the container process directly using signal from signals_sequence.

So the name is IMO correct and using `False` seems better to me (faster) than using some string value. It's also documented in the main loop, where I check for False.