Now that nodepool images are on quay.io we don't get speculative
container image testing with docker. The reason for this is docker only
knows how to lookup images hosted by docker.io in mirrors which
specualtive container image testing relies on. Since the images are
hosted on quay.io instead of docker.io we lose this functionality.
Address this by switching to podman and podman-compose which does
understand how to fetch images with mirrors from any location.
Depends-On: https://review.opendev.org/c/zuul/zuul/+/687135
Change-Id: I1a510a9b68a2f01098f3c099a129d6d268b422d9
5702331087