'Unrescue the specified instance.'

def unrescue(self, instance, power_on=True):

    vm_ref = vm_util.get_vm_ref(self._session, instance)
    try:
        rescue_device = self._get_rescue_device(instance, vm_ref)
    except exception.NotFound:
        with excutils.save_and_reraise_exception():
            LOG.error('Unable    to    access    the    rescue    disk', instance=instance)
    vm_util.power_off_instance(self._session, instance, vm_ref)
    self._volumeops.detach_disk_from_vm(vm_ref, instance, rescue_device, destroy_disk=True)
    if power_on:
        vm_util.power_on_instance(self._session, instance, vm_ref=vm_ref)
