Disable a config test if ran under the root user

The `test_conf_file_permission_denied` is designed to test
if a config file can't be read due to missing file permissions.

However if we run unit tests with the root user we will beneficiat
from the root privileges and so this test will fails. This can
be reproduced by running `tox` with `sudo`.

These changes propose to skip this test if root privileges are
detected.

Closes-bug: #1983358

Change-Id: Idd124082265032c30f83242b612d002d7093aa61
(cherry picked from commit 7b838f5c31)

oslo_config/tests/test_cfg.py

@@ -21,6 +21,7 @@ import os
 import shutil
 import sys
 import tempfile
+import unittest
 from unittest import mock
 
 import fixtures
@@ -3839,6 +3840,8 @@ class SadPathTestCase(BaseTestCase):
         self.assertRaises(cfg.ConfigFilesNotFoundError,
                           self.conf, ['--config-file', path])
 
+    @unittest.skipIf(os.getuid() == 0,
+                     "Not supported with the root privileges")
     def test_conf_file_permission_denied(self):
         (fd, path) = tempfile.mkstemp()