RHCS6 - Upgrade from RHCS5 to RHCS6 fails with "/usr/bin/podman: stderr Error: initializing source docker://registry.redhat.io/rhceph/rhceph-6-rhel8:latest"

Issue

During upgrade from RHCS 5.3 to RHCS 6.0 following the documentation we are getting following error:

# ceph orch upgrade check registry.redhat.io/rhceph/rhceph-6-rhel8:latest
Error EINVAL: host athos `cephadm pull` failed: cephadm exited with an error code: 1, stderr:Pulling container image registry.redhat.io/rhceph/rhceph-6-rhel8:latest...
Non-zero exit code 125 from /usr/bin/podman pull registry.redhat.io/rhceph/rhceph-6-rhel8:latest --authfile=/etc/ceph/podman-auth.json
/usr/bin/podman: stderr Trying to pull registry.redhat.io/rhceph/rhceph-6-rhel8:latest...
...
/usr/bin/podman: stderr Error: initializing source docker://registry.redhat.io/rhceph/rhceph-6-rhel8:latest: reading manifest latest in registry.redhat.io/rhceph/rhceph-6-rhel8: unknown: Not Found