Comment 4 for bug 1800601

Reviewed: https://review.openstack.org/615124
Committed: https://git.openstack.org/cgit/openstack/glance/commit/?id=43587fb93d8d949d9a9895153ac06ea4e7e6d150
Submitter: Zuul
Branch: master

commit 43587fb93d8d949d9a9895153ac06ea4e7e6d150
Author: James Page <email address hidden>
Date: Fri Nov 2 10:10:49 2018 +0000

    py3: fix recursion issue under py37

    Add tox target and resolve issue with infinite recursion in
    ExtraProperties class by directly using methods on the dict
    class.

    Closes-Bug: 1800601

    Change-Id: Ie98c4287c8bd1c364655adb99c7a88d1d451496e