ci: rework testing farm to use cloud takeover, not libvirt

[cgwalters]

Today our packit/tmt/testing-farm code ends up using the bootc provisioner which uses libvirt. In some cases this is convenient.

However, I think we should try to actually switch over to a replace workflow by default. This would have more impact on the tmt side I think, but it should dramatically improve the reliability and flexibility of our CI because we'll drop out bare metal (or at least nested virt) requirements.

(The nested virt is a whole separate thing to try to get into testing farm)