test_integration.config: Do not save the input environment
    
    Using the input environment saved in self._session_env
    outside of the config loading meant that methods of
    configuration other than environment variables wouldn't
    be possible.
    
    Restructure the roles/extra_roles to not depend on _session_env.
    
    Part of the work for: https://fedorahosted.org/freeipa/ticket/3938
    
    Reviewed-By: Tomas Babej <tbabej@redhat.com>