core: sanity check for cluster's quota

If quota mode is enforced, we should fail action in case
no quota is provided.
This bug was hidden from UI, and discovered via REST, since
there is a client validation for it.

The original bug was opened only for AddVmFromScratch,
Added this missing check also to:
*AddVm
*AddVmFromTemplate
*AddVmFromSnapshot
*AddVmTemplate

Change-Id: I0ef84ca9603a16014edaa4ddf99dfaa2f31744d4
Bug-Url: https://bugzilla.redhat.com/909749
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>