Demonstrate HTTP2 client is racy.

Don't merge.  Demonstrates that HTTP2 client is racey.  The client needs something to block on / wait for before attempting to send its first query.  It has no way of knowing whether or not the server has sent settings yet.

Repro: run Http2Server.  Repeatedly run Http2Client.  It fails every time.  Without the Thread.sleep() it only fails the first time for me locally.