set auth_uri and auth_host properly

as per https://bugs.launchpad.net/openstack-chef/+bug/1207504 auth_uri
must ALWAYS be set to the service endpoint and auth_host to the admin
endpoint

this also gets rid of:
WARNING keystoneclient.middleware.auth_token [-] Configuring auth_uri to point to the public identity endpoint is required; clients may not be able to authenticate against an admin endpoint