When import backup resource, cinder doesn't consume any backup related quotas, but when the imported backup resource is deleted, the quota will be decreased.
Step to reproduce:
1. import backup and show quota usage:
```
➜ ~ cinder backup-import cinder.backup.drivers.swift.SwiftBackupDriver 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
+----------+--------------------------------------+
| Property | Value |
+----------+--------------------------------------+
| id | 2c8c78bb-3908-4284-aee9-234448b2bf4a |
| name | None |
+----------+--------------------------------------+
➜ ~ cinder quota-usage ea2e3ae4fdd84472b6332df15bafaf85
+----------------------+--------+----------+-------+-----------+
| Type | In_use | Reserved | Limit | Allocated |
+----------------------+--------+----------+-------+-----------+
| backup_gigabytes | 0 | 0 | 1000 | |
| backups | 0 | 0 | 10 | |
| gigabytes | 0 | 0 | 1000 | |
| groups | 0 | 0 | 10 | |
| per_volume_gigabytes | 0 | 0 | -1 | |
| snapshots | 0 | 0 | 10 | |
| volumes | 0 | 0 | 10 | |
+----------------------+--------+----------+-------+-----------+
```
2. create a new backup and show quota usage:
```
cinder backup-create 3a8c6127-a5ea-4179-b969-0ca1f7f009ea
+-----------+--------------------------------------+
| Property | Value |
+-----------+--------------------------------------+
| id | efbd7f3a-06ea-4ae1-ad17-61f8c8b2ef69 |
| name | None |
| volume_id | 3a8c6127-a5ea-4179-b969-0ca1f7f009ea |
+-----------+--------------------------------------+
➜ ~ cinder backup-list
+--------------------------------------+--------------------------------------+-----------+------+------+--------------+---------------+
| ID | Volume ID | Status | Name | Size | Object Count | Container |
+--------------------------------------+--------------------------------------+-----------+------+------+--------------+---------------+
| 2c8c78bb-3908-4284-aee9-234448b2bf4a | a86491b9-26e5-4aff-8390-f48cb27096a6 | available | - | 1 | 22 | volumebackups |
| efbd7f3a-06ea-4ae1-ad17-61f8c8b2ef69 | 3a8c6127-a5ea-4179-b969-0ca1f7f009ea | available | - | 1 | 22 | volumebackups |
+--------------------------------------+--------------------------------------+-----------+------+------+--------------+---------------+
➜ ~ cinder quota-usage ea2e3ae4fdd84472b6332df15bafaf85
+----------------------+--------+----------+-------+-----------+
| Type | In_use | Reserved | Limit | Allocated |
+----------------------+--------+----------+-------+-----------+
| backup_gigabytes | 1 | 0 | 1000 | |
| backups | 1 | 0 | 10 | |
| gigabytes | 1 | 0 | 1000 | |
| groups | 0 | 0 | 10 | |
| per_volume_gigabytes | 0 | 0 | -1 | |
| snapshots | 0 | 0 | 10 | |
| volumes | 1 | 0 | 10 | |
+----------------------+--------+----------+-------+-----------+
```
3. delete imported backup resource and show quota usage:
```
cinder backup-delete 2c8c78bb-3908-4284-aee9-234448b2bf4a
Request to delete backup 2c8c78bb-3908-4284-aee9-234448b2bf4a has been accepted.
➜ ~ cinder quota-usage ea2e3ae4fdd84472b6332df15bafaf85
+----------------------+--------+----------+-------+-----------+
| Type | In_use | Reserved | Limit | Allocated |
+----------------------+--------+----------+-------+-----------+
| backup_gigabytes | 0 | 0 | 1000 | |
| backups | 0 | 0 | 10 | |
| gigabytes | 1 | 0 | 1000 | |
| groups | 0 | 0 | 10 | |
| per_volume_gigabytes | 0 | 0 | -1 | |
| snapshots | 0 | 0 | 10 | |
| volumes | 1 | 0 | 10 | |
+----------------------+--------+----------+-------+-----------+
```
Fix proposed to branch: master
Review: https:/