No need to use err1 and err2, because there is no mode like in
TestChdirAndGetwd (from os/os_test.go). Also, call fd.Close() via defer.

Change-Id: I8e57acbb382f072c48805f8931c464a169203512
Reviewed-on: https://go-review.googlesource.com/84476
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>