delete snapshot check in ceph

[Maksym Shalamov]

Issue described in [1] is reproduced on MOS 8.0. Description from [1] is listed below:

When rbd_flatten_volume_from_snapshot is set to false, a volume which is created from a snapshot in ceph has dependent upon the snapshot.
As a result, the snapshot can't be deleted with a reason "Delete snapshot failed, due to snapshot busy."
This is not clear. From Openstack, it is hard to find the dependency.
I would like to do the following work to make the error clear:
1. Check the dependency using ceph interface.
2. Add error message.

Found on:

VERSION:
  feature_groups:
    - mirantis
  production: "docker"
  release: "8.0"
  api: "1.0"
  build_number: "569"
  build_id: "569"
  fuel-nailgun_sha: "558ca91a854cf29e395940c232911ffb851899c1"
  python-fuelclient_sha: "4f234669cfe88a9406f4e438b1e1f74f1ef484a5"
  fuel-agent_sha: "658be72c4b42d3e1436b86ac4567ab914bfb451b"
  fuel-nailgun-agent_sha: "b2bb466fd5bd92da614cdbd819d6999c510ebfb1"
  astute_sha: "b81577a5b7857c4be8748492bae1dec2fa89b446"
  fuel-library_sha: "33634ec27be77ecfb0b56b7e07497ad86d1fdcd3"
  fuel-ostf_sha: "3bc76a63a9e7d195ff34eadc29552f4235fa6c52"
  fuel-mirror_sha: "fb45b80d7bee5899d931f926e5c9512e2b442749"
  fuelmenu_sha: "78ffc73065a9674b707c081d128cb7eea611474f"
  shotgun_sha: "63645dea384a37dde5c01d4f8905566978e5d906"
  network-checker_sha: "a43cf96cd9532f10794dce736350bf5bed350e9d"
  fuel-upgrade_sha: "616a7490ec7199f69759e97e42f9b97dfc87e85b"
  fuelmain_sha: "d605bcbabf315382d56d0ce8143458be67c53434"

[1] https://bugs.launchpad.net/cinder/+bug/1463682

[Maksym Shalamov (mshalamov)]

ERROR Message from cinder log file
cinder-volume: 2016-02-18 12:37:33.378 1067 ERROR cinder.volume.manager [req-ef24b7a5-1966-4cc3-9e14-446bb710d327 c40cf6ea7ff64d78b6316aa1952dc301 4e22293961b74619a0590aa484e26b0c - - -] Delete snapshot failed, due to snapshot busy.

[Roman Podoliaka (rpodolyaka)]

No longer fixing Wishlist bugs in 8.0, closing as Won't Fix.

[Ivan Kolodyazhny (e0ne)]

It's a feature request and will be fixed in upstream in scope of https://review.openstack.org/#/c/274958/

[Yuriy Nesenenko (ynesenenko)]

It's a feature request and will be fixed in upstream in scope of https://review.openstack.org/#/c/273938/

[Andres Toomsalu (andres-active)]

Setting rbd_flatten_volume_from_snapshot=True does not seem to have any effect in MOS 9.0:

https://bugs.launchpad.net/cinder/+bug/1485897/comments/4