Comment 19 for bug 1653953

Reviewed: https://review.opendev.org/668119
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=e93bc57a73d8642012f759a4ffbe5289112ba490
Submitter: Zuul
Branch: stable/rocky

commit e93bc57a73d8642012f759a4ffbe5289112ba490
Author: rsritesh <email address hidden>
Date: Wed Apr 19 12:02:30 2017 +0530

    libvirt: flatten rbd images when unshelving an instance

    Previously attempts to remove the shelved snapshot of an unshelved
    instance when using the rbd backends for both Nova and Glance would
    fail. This was due to the instance disk being cloned from and still
    referencing the shelved snapshot image in Glance, blocking any attempt
    to remove this image later in the unshelve process.

    After much debate this change attempts to fix this issue by flattening
    the instance disk while the instance is being spawned as part of an
    unshelve. For the rbd imagebackend this removes any reference to the
    shelved snapshot in Glance allowing this image to be removed. For all
    other imagebackends the call to flatten the image is currently a no-op.

    Co-Authored-By: Lee Yarwood <email address hidden>
    Co-Authored-By: Vladyslav Drok <email address hidden>

    Closes-Bug: #1653953
    Change-Id: If3c9d1de3ce0fe394405bd1e1f0fa08ce2baeda8
    (cherry picked from commit d89e7d7857e0ab56c3b088338272c24d0618c07f)
    (cherry picked from commit e802ede4b30b21c7590620abc142300a57bcf349)