Comment 7 for bug 1580625

Reviewed: https://review.openstack.org/315596
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=8b256fb50a0bb9c6ddcbff2099a744045688b652
Submitter: Jenkins
Branch: stable/mitaka

commit 8b256fb50a0bb9c6ddcbff2099a744045688b652
Author: Nicolas Simonds <email address hidden>
Date: Wed May 11 10:52:52 2016 -0700

    imagebackend: Check that the RBD image exists before trying to cleanup

    In volume-backed setups, there is no image to clean up, so any
    attempts to cleanup the resize snapshots will fail by definition.
    Make sure the image exists first.

    NOTE(mriedem): The backport has to add an additional mock that wasn't
    in the original change because on master the fake_imagebackend.Raw
    object wasn't used, simply a mock.Mock object which handled the
    check_image_exists() method call on the fake image backend.

    Change-Id: I25f65bcc76b83f31a8fce77c2b751d2d167ffc7e
    Closes-Bug: 1580625
    (cherry picked from commit 671bb2651d9d1a07947690468825581d30482dcb)