NFS Backup driver doesn't remove empty directories on backup deletion

[Rajat Dhasmana]

Using cinder backup with NFS backend, everything works fine, except that when we delete a backup the actual "content" of the backup gets deleted but not the directory structure on the NFS share.

(overcloud) [stack@undercloud-0 ~]$ openstack volume backup list --long --all-projects -c Container -c ID
+--------------------------------------+
| ID | Container |
+--------------------------------------+
| <id> | 17/ae/<path> |
+--------------------------------------+

[backups]# ll
total 0
drwxr-xr-x. 3 root root 16 Feb 2 06:28 02
drwxr-xr-x. 3 root root 16 Feb 2 06:33 17
drwxr-xr-x. 3 root root 16 Feb 2 06:19 5a
drwxr-xr-x. 3 root root 16 Feb 2 06:20 e4
drwxr-xr-x. 3 root root 16 Feb 2 06:32 e6

The only available volume backup is <id> in directory 17/ae and the rest of the backups were deleted yet their corresponding directories are still present. There is no content in the deleted volume backup directories.

[Rajat Dhasmana (whoami-rajat)]

Fix: https://review.opendev.org/c/openstack/cinder/+/804603