CVE-2016-2019: s3:selftest: add regression tests for guest logins and mandatory signing

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11860

Signed-off-by: Stefan Metzmacher <metze@samba.org>

Autobuild-User(master): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(master): Thu Jul  7 14:52:20 CEST 2016 on sn-devel-144
