Certain environment variables can influence the behavior of ssh-agent,
causing the test to fail. Avoid that influence by using a consistent
environment.
This fixes a locally-observed test failure for me.
Change-Id: I0f5e8d643199519f88e80825335ee8e6eb08e3af
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/207901
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>