Comment 5 for bug 1818730

Reviewed: https://review.openstack.org/648688
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=bcb42a43a9f12d929ec7025f29bd2e3d482cd406
Submitter: Zuul
Branch: stable/stein

commit bcb42a43a9f12d929ec7025f29bd2e3d482cd406
Author: Matt Riedemann <email address hidden>
Date: Tue Mar 5 16:39:51 2019 -0500

    Temporarily mutate migration object in finish_revert_resize

    As the comment in the code suggests, when calling migrate_instance_finish
    in finish_revert_resize we need to temporarily set the migration
    object dest_compute to the source_compute since we are moving port
    bindings from the dest back to the source. However, this is not
    really a temporary change to the object if something fails after
    this because the @errors_out_migration decorator will persist the
    change which could be confusing later if trying to debug this migration
    from the API and the dest_compute and source_compute have the same value.

    This fixes the issue by using the temporary_mutation utility.

    Also, the obj_to_primitive dance in here is removed since it is not
    necessary as migrate_instance_finish handles a Migration object.

    Change-Id: I312d61383345ea0ac1ab0c277b4c468e6aa94656
    Closes-Bug: #1818730
    (cherry picked from commit 855b5546564f0ed96243623b67b1322e9b891c8b)