core: Fix UpdateVm permissions check for Quota

Quota permissions were checked regardless of the vm state
(running/stopped), the quota enforcement mode (Audit/enforcing) and the
change in quota selection box.

addQuotaPermissionSubject was change to check for quota consumption permissions only
if the quota was changed & quota is Enforced & vm is running.
Otherwise, User could edit vm without having quota consumption
permissions.

Change-Id: Ib55016efcbed22b003eaddf5c4f8f62aec88928e
Bug-Url: https://bugzilla.redhat.com/904105
Signed-off-by: Ofri Masad <omasad@redhat.com>