Comment 4 for bug 1534655

At present, the only way to make the novaclient Python API work with keystone v3 is to construct a keystoneclient Session object and pass it to novaclient Client when creating the client object.

From comment #11 on bug 1522402:

"http://docs.openstack.org/developer/python-novaclient/api.html#usage

Note that you must create a Session object and pass it to novaclient.Client(session=<session object>) when creating the novaclient object. If you don't, novaclient will fall back on its own code for keystone auth and will NOT work with keystone v3."