The same edge cases that fail with other handshake methods
also fail here (mostly bad preface/timeouts stuff). In
addition, the HTTP2-Settings header contents are currently
not checked and so the related edge case tests also fail.
Currently only testing handshake.
Tests that pass currently involve no request/response.
ALPN and prior knowledge support have some edge cases left to fix.
HTTP/1.1 Upgrade has not been implemented yet.