s4-torture: Add handlers to block channels for testing

s4-torture: Add handlers to block channels for testing

We use two methods to block channels

1) Simply ignore incoming oplock break requests and do not respond to
them.
This method doesn't work against Microsoft Windows based servers which
rely on the tcp stack for confirmation that the oplock break command was
sent to the client machine. This is meant to be used with samba servers
and is the default method.

2) Use iptables to block the channel.
The method requires the use of a privileged account and can only be used
on Linux systems with iptables installed. To use this blocking method,
pass the option
--option=torture:use_iptables=true

Signed-off-by: Guenther Deschner <gd@samba.org>
Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Reviewed-by: Jeremy Allison <jra@samba.org>