Configure Keystone to allow OAuth authentication

Need https://review.openstack.org/#/c/95778/

We will also need to add this in infra when we have functionnal
tests using it

Part of blueprint solum-oauth
https://blueprints.launchpad.net/solum/+spec/solum-oauth

Change-Id: I45d2cc002ed6c7c99be43ff4d4ff8b1334db226a