All modifications to have a systemd ready container.

As systemd is mounting tmpfs in /tmp, I had to move the artifacts
repository to /opt/repo (which is anyway better).
Default entry point in the container is systemd and I added /etc/rc.local entry point for systemd containers.
Initially it is pulled from a shared mount on the kubelet running the
pod.
This commit is compatible with the standard way of running CI jobs,
following sytemd commits may break retrocompatibility.