This test is regularly failing on the plan9/386
builder running on GCE, but we haven't figured
out the issue yet.

Updates #26945.

Change-Id: I8cbe0df43c0757e7bc68e370311f4a28cd7b049b
Reviewed-on: https://go-review.googlesource.com/c/152721
Run-TryBot: David du Colombier <0intro@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>