Comment 2 for bug 1756151

Reviewed: https://review.openstack.org/553857
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=0372d82c2c5ae5651b00c5ab9e1cf5c77a8f87d9
Submitter: Zuul
Branch: master

commit 0372d82c2c5ae5651b00c5ab9e1cf5c77a8f87d9
Author: Chris Dent <email address hidden>
Date: Fri Mar 16 16:54:14 2018 +0000

    Ensure that os-traits sync is attempted only at start of process

    Traits sync had been tried any time a request that might involve
    traits was called. If the global was set no syncing was done, but
    lock handling was happening.

    This change moves the syncing into the the deploy.load_app() handling.
    This means that the syncing will be attempted any time a new WSGI
    application is created. Most of the time this will be at the start of a
    new process, but some WSGI servers have interesting threading models so
    there's a (slim) possibility that it could be in a thread. Because of
    this latter possibility, the locking is still in place.

    Functional tests are updated to explicitly do the sync in their
    setUp(). Some changes in fixtures are required to make sure that
    the database is present prior to the sync.

    While these changes are not strictly part of extracting placement, the
    consolidation and isolation of database handling code makes where to put
    this stuff a bit cleaner and more evident: an update_database() method
    in deploy uses an empty DbContext class from db_api to the call the
    ensure_trait_sync method in resource_provider. update_database is in
    deploy because it an app deployment task and because putting it in
    db_api leads to circual import problems.

    blueprint placement-extract
    Closes-Bug: #1756151

    Change-Id: Ic87518948ed5bf4ab79f9819cd94714e350ce265