Comment 15 for bug 1781300

Reviewed: https://review.opendev.org/686276
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=20de81c7c0dfe234805fa9552b1b83f3ea6df7a1
Submitter: Zuul
Branch: stable/rocky

commit 20de81c7c0dfe234805fa9552b1b83f3ea6df7a1
Author: Matt Riedemann <email address hidden>
Date: Thu Sep 13 13:28:24 2018 -0400

    Noop CantStartEngineError in targets_cell if API DB not configured

    For reschedules during resize (migrate_server method),
    the InstanceMapping query in targets_cell is an "up call"
    to the API DB which will fail with a CantStartEngineError
    if the cell conductor is not configured for the API DB.

    This changes the targets_cell decorator to handle the
    CantStartEngineError and if the API DB is not configured,
    we assume we're in the cell conductor and just ignore the
    error, otherwise if the API DB is configured we assume
    we're in the super-conductor and reraise as before.

    Change-Id: I0a413eb4f8a94500941e53b9a294d7cdb45d2a1c
    Closes-Bug: #1781300
    (cherry picked from commit 22dd4fca3837d6cea3f983b021aa6907695a540b)
    (cherry picked from commit d4bc147c38c5fe7c4adb5925225ced16d2ff4757)