Support auth urls which could be set separately

In Load-balanced auth urls, it would not just be openstack ip.
So, the user can export their openrc/openstackrc before running the test

Change-Id: Ic7e30187626e3b8fedada431c2cef9e5f365ebfb
Update references of auth_url to use OS_AUTH_URL

Change-Id: Icdc48a361a52e935389fed0db5c13e095fb03b03