core: Changed event message text on hotplug of CPUs

Changed event message text displayed at audit log during hotplug of
CPUs. Changed string and added the number of CPUs before change as well.

Change-Id: Iafb7134533975fe3f1d246e9106939c340868ecd
Bug-Url: https://bugzilla.redhat.com/1080364
Signed-off-by: Eldan Shachar <eshachar@redhat.com>