MEDIUM: checks: add send/expect tcp based check

MEDIUM: checks: add send/expect tcp based check

This is a generic health check which can be used to match a
banner or send a request and analyse a server response.
It works in a send/expect ways and many exchange can be done between
HAProxy and a server to decide the server status, making HAProxy able to
speak the server's protocol.

It can send arbitrary regular or binary strings and match content as a
regular or binary string or a regex.

Signed-off-by: Baptiste Assmann <bedis9@gmail.com>