Comment 3 for bug 1599256

Reviewed: https://review.openstack.org/342299
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=dc7c21f3cfbd5f68e9bc6b88f75e160826fadb82
Submitter: Jenkins
Branch: master

commit dc7c21f3cfbd5f68e9bc6b88f75e160826fadb82
Author: Pushkar Umaranikar <email address hidden>
Date: Thu Jul 14 17:32:02 2016 +0000

    Removing duplicates from columns_to_join list

    columns_to_join list contains duplicate values as we keep
    extending expected_attrs list in api level.
    This commit involves removing duplicates from columns_to_join
    attribute of instance model to avoid unnecessary joins in
    instance_get_all_by_filters method.
    Sorting resultant set based on list index is required to maintain
    the sequence.

    Change-Id: I2c93cef0babad23fa456bf10ba2ccaec7844b4cd
    Closes-Bug: #1599256