os: skip TestStatStdin on Android

Android doesn't (generally) have /bin/sh.

Change-Id: I343817c342e3473d09c85155761682b5ddb043e4
Reviewed-on: https://go-review.googlesource.com/21075Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/os/os_test.go

@@ -1584,8 +1584,9 @@ func TestStatDirModeExec(t *testing.T) {
 }
 
 func TestStatStdin(t *testing.T) {
-	if runtime.GOOS == "plan9" {
-		t.Skipf("skipping test on plan9")
+	switch runtime.GOOS {
+	case "android", "plan9":
+		t.Skipf("%s doesn't have /bin/sh", runtime.GOOS)
 	}
 
 	testenv.MustHaveExec(t)