http2: add disabled start of tests for trailers, clean up, deflake some tests

Sort response headers too, so we have consistent output.

Change-Id: I0ce925a8257a8e218a27b7d9b3fa9c96f71fba90
Reviewed-on: https://go-review.googlesource.com/17828
Reviewed-by: Blake Mizerany <blake.mizerany@gmail.com>
2 files changed