Deleting a server with volumes and delete_on_termination = true leaves running backups in creating state

[Robert Hoffmann]

If you create a backup of a volume attached to a server with delete_on_termination='True' and you delete the server (and the volume) before the backup is finished, the backup stays in creating status forever.

Can be reproduced by:

1. Create a server with volume attached and setting delete_on_termination='True'

2. Create a backup on this volume: openstack volume backup create --force volume_id
+-----------+--------------------------------------+
| Field | Value |
+-----------+--------------------------------------+
| id | 12345678-abcd-1234-1234-01234567890a |
| name | None |
| volume_id | 98765432-fedc-4321-4321-9876543210fe |
+-----------+--------------------------------------+

3. Delete the server: openstack server delete server_id

4. Check server is gone: openstack server show server_id
   No Server found for server_id

5. Check volume is gone: openstack volume show volume_id
   No volume with a name or ID of 'volume_id' exists.

6. Check backup: openstack volume backup show 12345678-abcd-1234-1234-01234567890a
+-----------------------+--------------------------------------------+
| Field | Value |
+-----------------------+--------------------------------------------+
...
| status | creating |