cinderclient auth issues with HTTPClient

There are a bunch of auth issues with cinderclient.client.HTTPClient which do not affect cinderclient.client.SessionClient. These should be addressed for the sake of things which still rely on HTTPClient.

1) the HTTPClient case lacks a way to pass an auth_token in on the __init__, which led to nova's horrible hack of setting it after the fact (before it switched to using sessions... see https://bugs.launchpad.net/nova/+bug/1401437).
2) Once it is possible to specify an auth_token on __init__ (see #1), HTTPClient should stop requiring auth_url be passed in when retries is None or 0, since at that point auth_url will only be used on retries.
3) HTTPClient's authenticate() method doesn't support keystone v3. Since https://review.openstack.org/#/c/95305/ purports to add keystone v3 support to cinderclient, but didn't address that method, I assume whoever wrote that expects SessionClient to be used instead of HTTPClient when using keystone v3. That seems like an invalid assumption, though, or at least something that should be checked and a nice error returned in the event that keystone v3 was tried.