engine: Disallow cross-DC template creation

Now we check during creation of template whether the target cluster
lies on the same storage domain as the source VM even if the template
contains no disks.

Change-Id: I6d9943ce1fb3736f280aaecc93896fc174c6b7dd
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1098951
Signed-off-by: Martin Betak <mbetak@redhat.com>