keystone_user_role provider should be `domain` aware

[Vasyl Saienko]

With keystone V3 API and multidomains support `user_name` attribute is no longer globally unique. It is rather `domain` unique .
keystone_user_role should receive `domain_name` and `user_name` in order to clearly define user.

[Richard Megginson (rmeggins)]

This is already supported with the current code. You specify it like this::

    keystone_user_role { 'username::user_domain_name@projectname::project_domain_name': }

This assumes you have the following resources defined in your manifest::

    keystone_tenant { 'projectname::project_domain_name': ...}
    keystone_user { 'username::user_domain_name': ...}