core: Allow updating wipeAfterDelete for an UP VM

The wipeAfterDelete property simply determines how the VM's volumes
should be treated when they are deleted, and has no effect on how the VM
is run.
There is no reason to disallow updating them when the VM is running.

Change-Id: I8fcb93ab0e45798745e2e5accc2d851b6df00d6d
Bug-Url: http://bugzilla.redhat.com/1103679
Signed-off-by: Allon Mureinik <amureini@redhat.com>