Allow cinder operations with only auth_token

Allow cinder operations with only auth_token

This uses the same technique as Horizon for auth_token operations.

Specifically, the cinder endpoint is found directly from keystone
and the auth_token and management_url are set on cinderclient
after it has been created.

Client libs are in theory capable of looking up their own endpoints
given an auth_token, but in practice this is the code-path least
travelled and there are many issues. I think it is best to do what
Horizon does, since all Horizon operations use only a token and always
provide the endpoint to the client lib.

Tested by launching a stack with and without the --token-only flag

Also tested using Horizon, which is auth_token only

Part of blueprint auth-token-only

Change-Id: Iea9159299ad3f354bcc768c9ac1172d6d9f814a8