tests: fix test_ipalib.test_frontend.test_Object
Update the fake API object to match the real API object interface including
the changes introduced with the API compatibility feature.
https://fedorahosted.org/freeipa/ticket/6188
Reviewed-By: Petr Spacek <pspacek@redhat.com>
Reviewed-By: Martin Basti <mbasti@redhat.com>