Comment 3 for bug 1297052

The reason is function in conductor/manager.py
def _cold_migrate
        ....
        except exception.NoValidHost as ex:
            vm_state = instance['vm_state']
            if not vm_state:
                vm_state = vm_states.ACTIVE
            updates = {'vm_state': vm_state, 'task_state': None}
            self._set_vm_state_and_notify(context, 'migrate_server',
                                          updates, ex, request_spec)
            if reservations:
                self.quotas.rollback(context, reservations)

            LOG.warning(_("No valid host found for cold migrate"),
                        instance=instance)
            return ----> return without any notification, so upper layer thought it succeed