add a new functionality to the agnhost image to run a server that
closes the connections received by sending a RST.
If a TCP servers closes the connection before all the socket is read,
it sends a RST. This implementations just reads only one byte from the
connection and closes it after that, that means that in order for this
to work the client has to send at least 2 bytes of data.
Using a simple curl is enough to trigger a RST:
curl http://127.0.0.1:8080
curl: (56) Recv failure: Connection reset by peer
Change-Id: I238fba0f790f2c92b37c732f51910a8b125f65db
