ceph-defaults: use podman on Fedora only
ceph-defaults: use podman on Fedora only

It seems Atomic 7.5 has podman already, however this is an old version
(0.4). The podman integration is targetting RHEL 8, so Fedora is
currently the closest to that.

Signed-off-by: Sébastien Han <62d754cc350e84d3b1c32ae79f976f5348e74a40@redhat.com>

fgal/ceph-ansible,ceph/ceph-ansible,ceph/ceph-ansible,fgal/ceph-ansible