core: Hot set number of CPUs using update VM

Hot plug and unplug a CPU to a running VM

* allow editing the number of cpus when the VM is UP
* if the VM is up and Version is > 3.3 call VDSM's  setNumberOfCpus
* audit log on success, failure

wiki: http://www.ovirt.org/Hot_plug_cpu

Bug-url: https://bugzilla.redhat.com/show_bug.cgi?id=1036777
Change-Id: I464a3dda5f143d1fcef63fd903eb615b01efe081
Signed-off-by: Roy Golan <rgolan@redhat.com>