cinder backup force-delete when backup is error

Update testcases to force delete a backup when the state is error

steps:
- create a backup
- reset backup state to error
- force delete the backup

Fixed create backup cleanup

Added API:
- force_delete_backup

Change-Id: I2495e9c10e888f5a01d2a3e7f09a4b6dfc3d58a0
diff --git a/releasenotes/notes/add-volume-backup-force-delete-af0156651a0cbf7f.yaml b/releasenotes/notes/add-volume-backup-force-delete-af0156651a0cbf7f.yaml
new file mode 100644
index 0000000..71bbfcb
--- /dev/null
+++ b/releasenotes/notes/add-volume-backup-force-delete-af0156651a0cbf7f.yaml
@@ -0,0 +1,9 @@
+---
+features:
+  - |
+    As in the [doc]:
+    https://developer.openstack.org/api-ref/block-storage/v3/
+    #force-delete-a-backup.
+
+      * Force-deletes a backup(v2)
+