For functions TestClonesRequestHeaders and TestReverseProxy_PanicBodyError,
I made changes to update the log verbosity.

Fixes #25634

Change-Id: I2a0ef70a8191cfb1a0005949345be722fb4ab62e
Reviewed-on: https://go-review.googlesource.com/115296Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>