ExecStopPost should allow us to clean up (docker kill + docker rm) even if the ExecStart (docker run ..) command failed, and not just after a graceful service stop was initiated. Source: https://www.freedesktop.org/software/systemd/man/systemd.service.html#ExecStopPost=
Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/683