This change updates the heat::keystone::auth class to include a default
service_name of 'heat' so that if a user changes the auth_name, the
service is still created as being related to 'heat'. This improves the
user experiance when they want to customize the usernames for services.
Closes-Bug: #1590040
Change-Id: Iee47e78dbeb269e5fe6c52030de378c13e51c1f3