selftests: sysinfo collects messages if available

The sysinfo.post collects "/var/log/messages" by default. This can fail
when not running as superuser. Adjust the unittests to handle booth
variants.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

selftests/all/unit/avocado/sysinfo_unittest.py

@@ -91,8 +91,10 @@ class SysinfoTest(unittest.TestCase):
         job_postdir = os.path.join(testdir, 'post')
         self.assertTrue(os.path.isdir(job_postdir))
         # By default, there are no post test files
-        self.assertEqual(len(os.listdir(job_postdir)), 0,
-                         "Test post dir is not empty")
+        self.assertLess(len(os.listdir(job_postdir)), 2,
+                        "Post dir can contain 0-1 files depending on whether "
+                        "sys messages are obtainable or not:\n%s"
+                        % os.listdir(job_postdir))
 
     def tearDown(self):
         shutil.rmtree(self.tmpdir)