Use keystone identity_uri instead of auth_*

Keystone middleware has deprecated the auth_host and friends in favor of
using identity_uri.

This was done in python-keystoneclient change:
I1f8f5064ea8028af60f167df9b97e215cdadba44

Change-Id: Ic43fc7656e63a890f25d0c8e9d2fed2213882b37
Merge "Use keystone identity_uri instead of auth_*"