smbcontrol: Use server_id_str_buf

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Martin Schwenke <martin@meltin.net>

Autobuild-User(master): Martin Schwenke <martins@samba.org>
Autobuild-Date(master): Wed Nov  5 13:03:39 CET 2014 on sn-devel-104