AWS helper to cleanup ephemeral objects created by other scripts

Other scripts should create VMs, SSH keys, and placement groups,
with tag isc:remove_after containing timestamp after which the object
should be forcefully removed. This script should be run periodically
to remove these "expired" objects.

This mechanism prevents us from burning money on forgotten leftover VMs.
E.g. when a Gitlab job is cancelled by user the Gitlab runner kills
everything and our scripts have no chance to cleanup things properly.

This script also limits cost of insufficient error handling in VM
orchestration etc.
1 job for aws-cleanup in 1 minute and 27 seconds (queued for 3 seconds)
Status Job ID Name Coverage
passed pylint #1897611
docker linux amd64