core: Upload only the DC diskless VMs/Templates to OVF stores

Since change Iaeecc6c4 OVF data of diskless VMs/Templates is uploaded to
all the DC domain.
The problem with that change is that the loaded VMs/Templates aren't
only for that data center - which is fixed in this change.

Change-Id: Ic51689cdf0479548c8c4be1267d478fcb8f89de0
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1138134
Signed-off-by: Liron Aravot <laravot@redhat.com>