x/net/http2: use request url scheme

The existing implementation has a hardcoded "https" scheme for
all request, since it allows http scheme in the request, it should
use the scheme in the request url.

Fixes golang/go#17257

Change-Id: Ibd9528df0328d7630ee94a006db694645625cdc9
Reviewed-on: https://go-review.googlesource.com/29975
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2 files changed