Comment 9 for bug 1860990

Reviewed: https://review.opendev.org/708615
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=b3afe748335886403315c6a7bba6a8879a05d077
Submitter: Zuul
Branch: stable/stein

commit b3afe748335886403315c6a7bba6a8879a05d077
Author: Vladyslav Drok <email address hidden>
Date: Mon Jan 27 15:31:53 2020 +0100

    Make RBD imagebackend flatten method idempotent

    If glance and nova are both configured with RBD backend, but glance
    does not return location information from the API, nova will fail to
    clone the image from glance pool and will download it from the API.
    In this case, image will be already flat, and subsequent flatten call
    will fail.

    This commit makes flatten call idempotent, so that it ignores already
    flat images by catching ImageUnacceptable when requesting parent info
    from ceph.

    NOTE(lyarwood): Conflict as I361af845d6a733618ecd056aa7df973191184ae9 is
    not present in stable/stein.

    Conflicts:
       nova/virt/libvirt/imagebackend.py

    Closes-Bug: 1860990
    Change-Id: Ia6c184c31a980e4728b7309b2afaec4d9f494ac3
    (cherry picked from commit 65825ebfbd58920adac5e8594891eec8e9cec41f)
    (cherry picked from commit 03d59e289369df4980bc1e7350e7f52a6f6aa828)