Comment 4 for bug 1639230

Reviewed: https://review.openstack.org/396782
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=bc620681ff2d7aa6c40c961da76d598c9f23281d
Submitter: Jenkins
Branch: stable/newton

commit bc620681ff2d7aa6c40c961da76d598c9f23281d
Author: Brent Tang <email address hidden>
Date: Fri Nov 4 07:35:25 2016 -0700

    Instance obj_clone leaves metadata as changed

    When performing an obj_clone on an Instance object, it relies on the
    base obj_clone's deep copy method which just goes through all of the
    fields and duplicates them on the clone. However, the Instance object
    has internal tracking attributes for metadata and system_metadata that
    keep track of which keys have changed. Since these don't get copied
    over on the deep copy, these will show up as having changed on the
    cloned Instance (if they had metadata set originally) and on a save
    on this cloned object will end up updating the metadata in the db
    which if these have stale information will wipe out other changes.

    Such a scenario to this is occurring during build_instance where the
    Claim constructor is saving off a clone of the Instance object
    so that it will have the current copy. In the case of a failure
    during the build_instance, the claim will use this current copy
    to then set the value of the host on the instance to None. Since
    the clone reflects that the system_metadata has changed, it will
    as part of the save try to update the system_metadata in the db,
    which since it is stale will wipe out changes made.

    In the case of the issue being fixed here, the value in the
    system_metdata being wiped out is the network_allocated=True
    attribute. By this being wiped out then reschedules of that
    build_instance fail in cases where the IP address has been
    assigned to the instance.

    Change-Id: Ie49a90993fb9643c04d75402dbaaa933c6b5222e
    Closes-Bug: #1639230
    (cherry picked from commit 9345ed40e85e291d2f9e9aac24d468f40140ae0e)