Create system test for sending many message sizes

[erikedin]

We've had issues with message sizes. I have no reason to believe that those issues aren't fixed, but I wouldn't feel bad if we had a system test for sending message of different sizes.

I imagine we send 100 001 messages from client to server, each message from size 0 to size 100 000.
That is, it'll start with size 0, then size 1, then size 2, and so on.