core: enable to decrease DC compatibility...

enable to decrease DC compatibility version if DC has no clusters

This patch enables to decrease the DC compatibility version if DC has no
clusters.

Change-Id: I73284f641b7f80b380b39efbbd7b4566f55119b6
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1057029
Signed-off-by: Eli Mesika <emesika@redhat.com>