MariaDB bootstrap has a phase where the first MariaDB container
is running with Galera bootstrap - after a check that WSREP
is synced is successful - we restart the container.

The bootstrap container is named mariadb and running with
docker_restart_policy: "no" - the restarted container should be running
in systemd.

Before this patch the code created a systemd unit but it was initially
stopped - so stopping was always a success - and the container would be
killed with SIGKILL on removal (which obviously breaks MariaDB).

This patch also improves docker/systemd stops by waiting for real
unit/container stop and adds failing CI for containers that are
killed with signal 9.

Closes-Bug: #2029613

Change-Id: I0a03e509ce228a50e081fcab44d2b4831251190c