Ceph » rbd

Steps to reproduce:
- create a mirroring image with data pool
- delete data pool
- try to remove image

It fails with the error:

2019-08-12T11:23:00.568+0100 7f1f93fff700 -1 librbd::image::RemoveRequest: 0x7f1f84002200 handle_mirror_image_remove: failed to remove mirror image state: (16) Device or resource busy
2019-08-12T11:23:00.600+0100 7f1fc7d66f40 -1 librbd::api::Trash: enable_mirroring: failed to retrieve features: (2) No such file or directory
Removing image: 0% complete...failed.

It is because the image open step fails due deleted data pool, and RemoveRequest skips many steps, one of them is disabling mirroring, and later it fails when trying to remove the image entry from rbd_mirror object.

As we do not have any guard to forbid data pool deletion if it is still in use, it would be nice to make `rbd remove` robust enough not to fail in such case.