core: Fix QuotaManager internal rollback

When two or more VDSGroup quota request were sent to the QuotaManager
together and one consumption request failed - the QuotaMAnager didnot
roll back the requests that already passed.

Added a rollback for the VDSGroup quotas if one request failed.

Change-Id: I3cee6810900c17f64d6ae47056969e656b1a4840
Bug-Url: https://bugzilla.redhat.com/950926
Signed-off-by: Ofri Masad <omasad@redhat.com>