s4:torture:samba3rpc: use an authenticated SMB connection and an anonymous DCERPC connection on top

This is the only way to get a reliable transport session key.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Günther Deschner <gd@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
