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>