ldb-samba: Add "secret" as a value to hide in LDIF files

ldb-samba: Add "secret" as a value to hide in LDIF files

This is not secret or encrypted in LDAP, but is sensitive in secrets.ldb

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
Autobuild-User(master): Garming Sam <garming@samba.org>
Autobuild-Date(master): Wed May 11 07:17:38 CEST 2016 on sn-devel-144

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12154

(cherry picked from commit 15f191a2329d08b92111f71e22f8a28c8a39c193)

Autobuild-User(v4-2-test): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(v4-2-test): Mon Aug 15 15:46:12 CEST 2016 on sn-devel-104