message: VN test, but just checks for connection closing
diff: @@ -470,6 +470,9 @@ impl Handler for VnHandler {
  }
  fn rewrite_out(&mut self, dgrams: &mut Vec<Datagram>) {
  + if dgrams.len() == 0 {
  + return
  + }
  assert!(dgrams.len() == 1);
  dgrams[0].d[1] = 0x1a;
  }
  @@ -499,8 +502,18 @@ fn run_test<'t>(peer: &Peer, test: &'t Test) -> (&'t Test, String) {
  };
  if let Test::VN = test {
  - let _res = test_vn(&nctx, peer);
  - unimplemented!();
  + let res = test_vn(&nctx, peer);
  + return match res {
  + Err(e) => (test, format!("ERROR: {}", e)),
  + Ok(client) => {
  + match client.state() {
  + State::Closing { .. } => {
  + (test, String::from("OK"))
  + },
  + _ => (test, format!("ERROR: Wrong state {:?}", client.state()))
  + }
  + }
  + }
  }
  let mut client = match test_connect(&nctx, test, peer) {
  @@ -582,8 +595,8 @@ const PEERS: [Peer; 9] = [
  },
  Peer {
  label: "applequic",
  - host: "192.168.203.142",
  - port: 4433,
  + host: "31.133.129.48",
  + port: 8443,
  },
  Peer {
  label: "f5",
  