Reactivate image before deletion

Normal users should not be able to delete disabled images (see [1])
as this can lead to inconsistencies between database and storage
backend.

Tempest relies on being able to do this in some tests.

[1]: https://bugs.launchpad.net/glance/+bug/1917469

Related-Bug: 1917469
Change-Id: I0b29fe59e238f4c723a15271117e6cfb072e648a
1 file changed