Adds a new zaqar::keystone::auth_websocket class to help
create a 'messaging-websocket' Keystone endpoint. Users of
zaqar websockets currently have to do substring replacement on the
Zaqar HTTP URLs... having a dedicated endpoint for websockets will
be much better.
Change-Id: Idd3ca1765604d9a461f68fc7b4a18b23a3c19d5b