util: implement kill switch for AsyncLoopSupervisor
util: implement kill switch for AsyncLoopSupervisor

Implement an unclean loop stop in AsyncLoopSupervisor to avoid any
possibility of indefinite hangs (although it should not happen any more
with the new Coordinator/Watcher setup). Set it just a bit higher than
the regular timeout by default.

Cobliteam/shelver,Cobliteam/shelver