Rust future/result and_then style control flow.

sample.rs

            open_server_stream().ok()
                .and_then(|stream| UnixStream::from_stream(stream, &handle).ok())
                .and_then(|stream| bind_and_send_client(stream, &handle, &tx_rpc))
                .ok_or_else(|| io::Error::new(
                    io::ErrorKind::Other,
                    "Failed to open stream and create rpc."
                ))