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 <lyarwood@redhat.com>
Co-Authored-By: Vladyslav Drok <vdrok@mirantis.com>
Closes-Bug: #1653953
Change-Id: If3c9d1de3ce0fe394405bd1e1f0fa08ce2baeda8
d89e7d7857