Comment 16 for bug 1784705

Reviewed: https://review.openstack.org/588076
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=d4179e3e96b3f3820b1055624ca81c441b94332e
Submitter: Zuul
Branch: stable/ocata

commit d4179e3e96b3f3820b1055624ca81c441b94332e
Author: Matt Riedemann <email address hidden>
Date: Tue Jul 31 16:00:28 2018 -0400

    Add recreate test for RT.stats bug 1784705

    With change I6827137f35c0cb4f9fc4c6f753d9a035326ed01b in
    Ocata, we changed the ComputeManager to manage a single
    ResourceTracker and that single ResourceTracker will
    manage multiple compute nodes. The only time a single
    nova-compute service hosts multiple compute nodes is for
    ironic where there is a compute node per instance. The
    problem is the ResourceTracker.stats variable, unlike the
    ResourceTracker.compute_nodes variable, is not node-specific
    so it's possible for node stats to leak across nodes based
    on how the stats are used (and copied).

    This change adds a functional recreate test to show the issue
    before it's fixed. The fixture setup had to be tweaked a
    bit to avoid modifying class variables by reference between
    test cases.

    Conflicts:
          nova/tests/functional/compute/test_resource_tracker.py

    NOTE(mriedem): The conflict is due to this test module not
    existing in Ocata. It was introduced in Pike with change
    I59be1cbedc99dcbb0ccde089a9f4737305176324 and changes were
    made to it over time. In this backport, the basics needed
    for the one test case specific to this patch are added and
    everything else, like the placement stuff, is removed.

    Change-Id: Icc5f615baa1042347ec1699eb84ba0670445b995
    Related-Bug: #1784705
    (cherry picked from commit fc05626d43571733da0803df0fd9a7c69766b8fd)
    (cherry picked from commit cc8167a1914a70ea7b336856285df2571a754ca0)
    (cherry picked from commit dbce613a9aede3fc5463a2d383b355ffb8cda73a)