core: update CPU QoS policy for running VMs

If a VM succeed to run and has CPU QoS attached, update
the vm policy.

Change-Id: Ia762ef4fc26cbfa913c077d34da51a9fa44946e8
Bug-Url: https://bugzilla.redhat.com/1084930
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>