'Destroys the source instance.'

def _confirm_resize(self, context, instance, migration=None):

    self._notify_about_instance_usage(context, instance, 'resize.confirm.start')
    with self._error_out_instance_on_exception(context, instance):
        old_instance_type = instance.old_flavor
        instance.old_flavor = None
        instance.new_flavor = None
        instance.system_metadata.pop('old_vm_state', None)
        instance.save()
        self.network_api.setup_networks_on_host(context, instance, migration.source_compute, teardown=True)
        network_info = self.network_api.get_instance_nw_info(context, instance)
        self.driver.confirm_migration(context, migration, instance, network_info)
        migration.status = 'confirmed'
        with migration.obj_as_admin():
            migration.save()
        rt = self._get_resource_tracker()
        rt.drop_move_claim(context, instance, migration.source_node, old_instance_type, prefix='old_')
        instance.drop_migration_context()
        p_state = instance.power_state
        vm_state = None
        if (p_state == power_state.SHUTDOWN):
            vm_state = vm_states.STOPPED
            LOG.debug("Resized/migrated    instance    is    powered    off.    Setting    vm_state    to    '%s'.", vm_state, instance=instance)
        else:
            vm_state = vm_states.ACTIVE
        instance.vm_state = vm_state
        instance.task_state = None
        instance.save(expected_task_state=[None, task_states.DELETING])
        self._notify_about_instance_usage(context, instance, 'resize.confirm.end', network_info=network_info)
