Revert "switch to using auth_url instead of auth_host et al"

This reverts commit 6d252ac4841d66eb3ced83bdce09db0e16c7f9b2.

keystone_authtoken middleware has no config option for auth_url,
so the change breaks neutron-server from being able to contact the
correct keystone service (unless it runs on localhost,
which is what auth_host defaults to)

Related-Bug: #1319280
Change-Id: I41a2ecd0ada3ec59983fd408123b0f3570050bb1