tests: Make pylint happy and fix python2.6 uses of assertRaisesRegex.

Older unittest2.TestCase (as seen in CentOS 6) do not have an
assertRaisesRegex method. They only have the now-deprecated
assertRaisesRegexp.

We need our unit tests to work there and on newer python (3.6).
Simply making assertRaisesRegex = assertRaisesRegexp makes pylint
complain as described in pylint-dev/pylint#1946 .

What was here before this commit was actually broken.  This commit
makes assertRaisesRegex functional in CentOS 6 and works around
the invalid Deprecated warning from pylint.

To prove this, we use assertRaisesRegex in a unit test which will
be exectued in py27, py3 and py26.

cloudinit/tests/helpers.py

@@ -433,12 +433,12 @@ def __mock_assert_not_called(mmock):
     mock.Mock.assert_not_called = __mock_assert_not_called
 
 
-# older unittest2.TestCase (centos6) do not have assertRaisesRegex
-# And setting assertRaisesRegex to assertRaisesRegexp causes
-# https://github.com/PyCQA/pylint/issues/1653 . So the workaround.
+# older unittest2.TestCase (centos6) have only the now-deprecated
+# assertRaisesRegexp. Simple assignment makes pylint complain, about
+# users of assertRaisesRegex so we use getattr to trick it.
+# https://github.com/PyCQA/pylint/issues/1946
 if not hasattr(unittest2.TestCase, 'assertRaisesRegex'):
-    def _tricky(*args, **kwargs):
-        return unittest2.TestCase.assertRaisesRegexp
-    unittest2.TestCase.assertRaisesRegex = _tricky
+    unittest2.TestCase.assertRaisesRegex = (
+        getattr(unittest2.TestCase, 'assertRaisesRegexp'))
 
 # vi: ts=4 expandtab

tests/unittests/test_handler/test_handler_apt_source_v1.py

@@ -569,7 +569,8 @@ def test_convert_to_new_format_collision(self):
         newcfg = cc_apt_configure.convert_to_v3_apt_format(cfg_3_only)
         self.assertEqual(newcfg, cfg_3_only)
         # collision (unequal)
-        with self.assertRaises(ValueError):
+        match = "Old and New.*unequal.*apt_proxy"
+        with self.assertRaisesRegex(ValueError, match):
             cc_apt_configure.convert_to_v3_apt_format(cfgconflict)
 
     def test_convert_to_new_format_dict_collision(self):