This pull request adds support for the OpenID Connect authentication
flow in Keystone and enables both ID and access token authentication
flows. The ID token configuration is designed to allow users to
authenticate via Horizon using an identity federation; whereas the
Access token is used to allow users to authenticate in the OpenStack CLI
using a federated user.

Without this PR, if one wants to configure OpenStack to use identity
federation, he/she needs to do a lot of configurations in the keystone,
Horizon, and register quite a good number of different parameters using
the CLI such as mappings, identity providers, federated protocols, and
so on. Therefore, with this PR, we propose a method for operators to
introduce/present the IdP's metadata to Kolla-ansible, and based on the
presented metadata, Kolla-ansible takes care of all of the
configurations to prepare OpenStack to work in a federated environment.

Implements: blueprint add-openid-support
Co-Authored-By: Jason Anderson <jasonanderson@uchicago.edu>
Change-Id: I0203a3470d7f8f2a54d5e126d947f540d93b8210