http2: fix broken tests
http2: fix broken tests

testServerResponse had dead code -- it was not checking the return
value from the handler func. This fix revealed two broken tests, which
were also fixed.

Change-Id: I7cd6f6c71dbd909fa3b0aff7f98a47dade42913b
Reviewed-on: https://go-review.googlesource.com/29434
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/net