Reduce potential hanging during manager termination

{width=1694 height=730}

We have a safety guard in aiotools to prevent making left-over processes (and we also use the “mixed-mode” in systemd configurations), but still any interruption signal should be gracefully handled in the manager coroutines. Particularly, we need to take extra care for periodic tasks in the scheduler not to defer cancellation for a too long time.

JIRA Issue: BA-488