cmd/go: skip TestGoInstallErrorOnCrossCompileToBin in short mode

That test will install cmd/pack for linux_386; we don't want to change
GOROOT in short mode.

Change-Id: I4b00c578a99779a13c558208bfd4115f8f0513fa
Reviewed-on: https://go-review.googlesource.com/12481
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/go_test.go

@@ -746,6 +746,10 @@ func TestGoInstallDetectsRemovedFiles(t *testing.T) {
 }
 
 func TestGoInstallErrorOnCrossCompileToBin(t *testing.T) {
+	if testing.Short() {
+		t.Skip("don't install into GOROOT in short mode")
+	}
+
 	tg := testgo(t)
 	defer tg.cleanup()
 	tg.tempFile("src/mycmd/x.go", `package main