This should fix the report at #16224, and also fixes running the test as
root on my Ubuntu Trusty system.

Fixes #16224.

Change-Id: I4e3b5527aa63366afb33a7e30efab088d34fb302
Reviewed-on: https://go-review.googlesource.com/24670
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>