Stop containers of running systems on `azk agent stop`

[fearenales]

When the agent is stopped by azk agent stop, the running systems aren't stopped, i.e. their containers keep running (check it using adocker ps after stopping azk agent).

Those lost containers are removed only when the agent is started:

. . .
azk: Cleaning 2 lost containers
. . .

My purpose is to run that cleaning routine on the azk agent stop as well.