Use except x as y instead of except x, y

According to https://docs.python.org/3/howto/pyporting.html the
syntax changed in Python 3.x. The new syntax is usable with
Python >= 2.6 and should be preferred to be compatible with Python3.

Enabled hacking check H231.

Change-Id: I2c41dc3ec83e79181e8fd50e76771a74c393269c

test/unit/account/test_reaper.py

@@ -543,7 +543,7 @@ class TestReaper(unittest.TestCase):
             with patch('swift.account.reaper.random.random', fake_random):
                 try:
                     r.run_forever()
-                except Exception, err:
+                except Exception as err:
                     pass
         self.assertEqual(self.val, 1)
         self.assertEqual(str(err), 'exit')

test/unit/cli/test_info.py

@@ -79,7 +79,7 @@ class TestCliInfoBase(unittest.TestCase):
     def assertRaisesMessage(self, exc, msg, func, *args, **kwargs):
         try:
             func(*args, **kwargs)
-        except Exception, e:
+        except Exception as e:
             self.assertTrue(msg in str(e),
                             "Expected %r in %r" % (msg, str(e)))
             self.assertTrue(isinstance(e, exc),

tox.ini

@@ -59,6 +59,6 @@ commands = {posargs}
 # H501 -> don't use locals() for str formatting
 # H903 -> \n not \r\n
 ignore = H
-select = F,E,W,H102,H103,H501,H903
+select = F,E,W,H102,H103,H501,H903,H231
 exclude = .venv,.tox,dist,doc,*egg
 show-source = True