contrib: add flag for docker hub status
contrib: add flag for docker hub status

Currently shields.io does not support tags but it's ongoing.
See progress here: https://github.com/badges/shields/issues/935

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

osixia/ceph-docker,cdxvirt/ceph-docker,JrCs/ceph-docker,ceph/ceph-docker,rootfs/ceph-docker,JrCs/ceph-docker,osixia/ceph-docker,mkkie/ceph-docker,JrCs/ceph-docker,osixia/ceph-docker,mkkie/ceph-docker,ceph/ceph-docker,rootfs/ceph-docker,cdxvirt/ceph-docker