os: do not test error case of TestRemoveAll when root

Fixes #22.

R=r1, r
https://golang.org/cl/152073

src/pkg/os/path_test.go

@@ -104,6 +104,7 @@ func TestRemoveAll(t *testing.T) {
 		t.Fatalf("Lstat %q succeeded after RemoveAll (second)", path)
 	}
 
+	if Getuid() != 0 {	// Test fails as root
 		// Make directory with file and subdirectory and trigger error.
 		if err = MkdirAll(dpath, 0777); err != nil {
 			t.Fatalf("MkdirAll %q: %s", dpath, err)
@@ -133,6 +134,8 @@ func TestRemoveAll(t *testing.T) {
 		if perr.Path != dpath {
 			t.Fatalf("RemoveAll %q failed at %q not %q", path, perr.Path, dpath)
 		}
+	}
+
 	if err = Chmod(dpath, 0777); err != nil {
 		t.Fatalf("Chmod %q 0777: %s", dpath, err)
 	}