samba-tool:provision: fix bug 11600

samba-tool:provision: fix bug 11600

If you join a second DC after changing the name of
the 'Default Domain Policy' or 'Default Domain Controllers
Policy' the join will fail as the search is hardcoded to
these names, this fix changes the search to the objects name.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11600

Signed-off-by: Rowland Penny <repenny241155@gmail.com>
Reviewed-by: Michael Adam <obnox@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Michael Adam <obnox@samba.org>
Autobuild-Date(master): Sat Nov 21 04:44:58 CET 2015 on sn-devel-104