Comment 3 for bug 1772088

Reviewed: https://review.openstack.org/569576
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=419e6198fadf4e91855109b76374d5205164b467
Submitter: Zuul
Branch: stable/queens

commit 419e6198fadf4e91855109b76374d5205164b467
Author: Dan Smith <email address hidden>
Date: Fri May 18 09:28:18 2018 -0700

    Make instance.refresh() avoid recursion better

    The instance.refresh() method is careful to prevent recursion, to avoid
    lazy-loads on the object we just pulled from the database. However, it
    was allowing those to raise OrphanedObjectError to the caller to make
    them visible. The caller is not really at fault in that case, and can not
    avoid it.

    The only time this has ever come up is in the context of cellsv1 and the
    keypairs field that it doesn't have set on instances in the child cells.
    Thus, this changes refresh() to just skip fields that are set on the
    current object and unset on the one we pull from the database, as we
    would not be able to refresh those anyway. This logs the situation so that
    it is visible (at DEBUG) if it becomes relevant.

    Closes-Bug: #1772088

    Change-Id: Ibfca4ae922766b5b977e217594d12e1169ddeee8
    (cherry picked from commit 549e5a2226ccf3920fd49e6726d5cea7fabf2914)