Fixes the os test on the Android builder.

Change-Id: Ibb9db712156a620fcccf515e035475c5e2f535a5
Reviewed-on: https://go-review.googlesource.com/33650
Run-TryBot: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>