Force nova to use keystone v2.0 for auth_token

This is a workaround for bug 1154809 until cinderclient supports
v3 service catalogs or we have some workaround in place.

Change-Id: I832ef1735579b240a367c051c44f97b1619f8d3d
Merge "Force nova to use keystone v2.0 for auth_token"