ceph: fix external cluster config override cm creation
ceph: fix external cluster config override cm creation

If an image is specified in the external cluster CR, the
'rook-ceph-config' config map will be created and then child CRs like
rgw/mds/nfs can be created.

Also, calling config.GetStore() was a mistake since it's calling by the
health check if new mons are being added to clusterInfo.

Closes: https://github.com/rook/rook/issues/4686
Signed-off-by: Sébastien Han <62d754cc350e84d3b1c32ae79f976f5348e74a40@redhat.com>

rook/rook,rook/rook,rook/nfs,rook/rook,rook/nfs,rook/rook,rook/rook,rook/nfs