Choose whether system containers etcd, kubernetes and the heat-agent will be
installed with podman or atomic. This label is relevant for k8s_fedora drivers.

k8s_fedora_atomic_v1 defaults to use_podman=false, meaning atomic will be used
pulling containers from docker.io/openstackmagnum. use_podman=true is accepted
as well, which will pull containers by k8s.gcr.io.

k8s_fedora_coreos_v1 defaults and accepts only use_podman=true.

Fix upgrade for k8s_fedora_coreos_v1 and magnum-cordon systemd unit.

Task: 37242
Story: 2005201

(cherry-picked from aa6b3bbe

)
Change-Id: I0d5e4e059cd4f0458746df7c09d2fd47c389c6a0
Signed-off-by: Spyros Trigazis <spyridon.trigazis@cern.ch>