Initialize novaclient auth system plugins, to handle changes to novaclient

Initialize novaclient auth system plugins, to handle changes from https://github.com/openstack/python-novaclient/commit/d195c6a6f7ca39c39e95c49220ed74ceb52f1afd

This adds the missed change from my last pull request.  I somehow missed it in the merge on my end, and it got left out.