OS-4374: set swarm mode osdistro to fedora-atomic

Ricardo Rocha requested to merge 4374-fixclusterdistro into cern-newton

Upstream name is fedora-atomic-swarm-mode to keep coe as swarm, but that means having two similar images with different osdistros. Set it to fedora-atomic in our setup as we don't care about legacy swarm anymore.

Closes #4374

Merge request reports