[release-branch.go1.6] syscall: disable TestGetfsstat failure on builders

The underlying bug is fixed on master.
We don't need to (nor want to) port the fix back,
but we do want to be able to run all.bash for
minor releases.

Change-Id: Ib612fc84fd8cd1f57456dd300855318badf97cf7
Reviewed-on: https://go-review.googlesource.com/33850


Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>