Description of problem: Since bug #1688098 we need more scenarios for full backups.
Description of problem: We need to add a new scenario for testing the new feature introduced in bug #1688098. Also, check those incremental backups have the right link to their parent backup (base image). Currently, we only have a test for a simple backup scenario. [1] Test steps: 1. Create a volume “v1”. 2. Create a full backup for v1 “b1”. 3. After that create an incremental backup for v1, “b2”. 4. Create a second full backup, called “b3”. 5. After that create a second incremental backup “b4”. 6. Delete b4, b3. 7. Create a third incremental backup “b5”. 8. Check that b2 can’t be deleted. 9. Check that b5 is incremental. [1] https://opendev.org/openstack/cinder-tempest-plugin/src/branch/master/cinder_tempest_plugin/api/volume/test_volume_backup.py#L71