net/http, reflect: rename Test function names

net/http, reflect: rename Test function names

To be consistent with other tests.

Change-Id: Ibea1d3bf57a295f024e05173d17112ce46a4f0bc
Reviewed-on: https://go-review.googlesource.com/c/go/+/585895
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Damien Neil <dneil@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>