Add trust users to AccessInfo and fixture

A trust should always contain a trustee_user_id and a trustor_user_id.
Expose these values via AccessInfo if available.

Change-Id: Ic46a44300e6bf8aa694f1543d470c16fcac643fc
Plugin loading from config objects

Provide a pattern for auth plugins to load themselves from a config
object. The first user of this will be auth_token middleware however it
is not likely to be the only user.

By doing this in an exportable way we are defining a single config file
format for specifying how to load a plugin for all services. We also
provide a standard way of retrieving a plugins options for loading via
other mechanisms.

Blueprint: standard-client-params
Change-Id: I353b26a1ffc04a20666e76f5bd2f1e6d7c19a22d
Allow loading auth plugins from CLI

With a standard definition of auth plugin options we should be able to
load and use those plugins from command line applications. Provide a
mechanism to register argparse parameters and load from them.

Blueprint: standard-client-params
Change-Id: I5d9904fa885602aaaef7a9e0afd4bd6bbfca3f07
Direct move of the revoke model from keystone server

This commit copies the revoke model from Keystone to
keystoneclient. The only difference in the model.py
file between keystoneclient and keystone is the
import due to a change of the oslo-incubator path
(project name is keystoneclient not keystone).

Blueprint: revocation-event-api

Change-Id: I6215d6679f9bb0dff6941c2a65ceeefd1ff9d88a
Merge "Direct move of the revoke model from keystone server"
Merge "Plugin loading from config objects"
Merge "Add trust users to AccessInfo and fixture"
Merge "Allow loading auth plugins from CLI"