container: use tmpfiles.d to creates /run/ceph

container: use tmpfiles.d to creates /run/ceph

instead of using `RuntimeDirectory` parameter in systemd unit files,
let's use a systemd `tmpfiles.d` to ensure `/run/ceph`.

Explanation:

`podman` doesn't create the `/var/run/ceph` if it doesn't exist the time
where the container is run while `docker` used to create it.
In case of `switch_to_containers` scenario, `/run/ceph` gets created by
a tmpfiles.d systemd file; when switching to containers, the systemd
unit file complains because `/run/ceph` already exists

The better fix would be to ensure `/usr/lib/tmpfiles.d/ceph-common.conf`
is removed and only rely on `RuntimeDirectory` from systemd unit file parameter
but we come from a non-containerized environment which is already running,
it means `/run/ceph` is already created and when starting the unit to
start the container, systemd will still complain and we can't simply
remove the directory if daemons are collocated.

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>