python: dsal: Fix possibility of identical ACE's being added.

python: dsal: Fix possibility of identical ACE's being added.

Currently it is possible to add the same ace multiple times if
the case sensitivity does not match the existing one using "--sddl" parameter.
As an example while an ace

"OA;CIIO;RPWP;3e978925-8c01-11d0-afda-00c04fd930c9;bf967a86-0de6-11d0-a285-00aa003049e2;PS"

already exists a sddl

"OA;CIIO;RPWP;3E978925-8C01-11D0-AFDA-00C04FD930C9;BF967A86-0DE6-11D0-A285-00AA003049E2;PS"

can be added without detection (and can be added multiple times). As an end result
after a high number of addings (in my tests it was about 1600-1800 aces for one
object) no further changes on that object are possible.

Signed-off-by: Martin Krämer <mk.maddin@gmail.com>
Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Rowland Penny <rpenny@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Fri Jan 18 23:19:13 CET 2019 on sn-devel-144