Test: hide expected stdout/stderr attributes

Now that 7c967bb0 hid the methods that record/check stdout/stderr,
let's also hide the attributes that hold their paths.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

avocado/core/test.py

@@ -90,9 +90,9 @@ class Test(unittest.TestCase):
 
         self.filename = inspect.getfile(self.__class__).rstrip('co')
         self.basedir = os.path.dirname(self.filename)
-        self.expected_stdout_file = os.path.join(self.datadir,
+        self._expected_stdout_file = os.path.join(self.datadir,
                                                   'stdout.expected')
-        self.expected_stderr_file = os.path.join(self.datadir,
+        self._expected_stderr_file = os.path.join(self.datadir,
                                                   'stderr.expected')
 
         if base_logdir is None:
@@ -323,23 +323,23 @@ class Test(unittest.TestCase):
 
     def _record_reference_stdout(self):
         utils_path.init_dir(self.datadir)
-        shutil.copyfile(self.stdout_file, self.expected_stdout_file)
+        shutil.copyfile(self.stdout_file, self._expected_stdout_file)
 
     def _record_reference_stderr(self):
         utils_path.init_dir(self.datadir)
-        shutil.copyfile(self.stderr_file, self.expected_stderr_file)
+        shutil.copyfile(self.stderr_file, self._expected_stderr_file)
 
     def _check_reference_stdout(self):
-        if os.path.isfile(self.expected_stdout_file):
-            expected = genio.read_file(self.expected_stdout_file)
+        if os.path.isfile(self._expected_stdout_file):
+            expected = genio.read_file(self._expected_stdout_file)
             actual = genio.read_file(self.stdout_file)
             msg = ('Actual test sdtout differs from expected one:\n'
                    'Actual:\n%s\nExpected:\n%s' % (actual, expected))
             self.assertEqual(expected, actual, msg)
 
     def _check_reference_stderr(self):
-        if os.path.isfile(self.expected_stderr_file):
-            expected = genio.read_file(self.expected_stderr_file)
+        if os.path.isfile(self._expected_stderr_file):
+            expected = genio.read_file(self._expected_stderr_file)
             actual = genio.read_file(self.stderr_file)
             msg = ('Actual test sdterr differs from expected one:\n'
                    'Actual:\n%s\nExpected:\n%s' % (actual, expected))