python/tests: add auth_pad test for the dcerpc raw_protocol test

python/tests: add auth_pad test for the dcerpc raw_protocol test

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11982

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Fri Jun 24 18:08:44 CEST 2016 on sn-devel-144

(cherry picked from commit c49f9abb19adca999d0b1d897d00d91f0ad91bbd)

Autobuild-User(v4-2-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-2-test): Thu Aug  4 13:43:46 CEST 2016 on sn-devel-104