http2 compat tests

[ronag]

Maybe we should have some tests against http2 compat? Also, I think some optimizations can be performed for the http2 case.

[dougwilson]

Yea, now that there are some Node.js releases with http2 flagged, seems like a good time to start. There are four main items that we probably want to detect finished state for I think:

1. Request
2. Response
3. The stream
4. The overall session

I will take a look and dig in soon :)