Replace assertItemsEqual with assertCountEqual

assertItemsEqual was removed from Python's unittest.TestCase in
Python 3.3 [1][2]. We have been able to use them since then, because
testtools required unittest2, which still included it. With testtools
removing Python 2.7 support [3][4], we will lose support for
assertItemsEqual, so we should switch to use assertCountEqual.

[1] - https://bugs.python.org/issue17866
[2] - https://hg.python.org/cpython/rev/d9921cb6e3cd
[3] - testing-cabal/testtools#286
[4] - testing-cabal/testtools#277

Change-Id: I1ad0da8deda3a8cbec384b5a9c88860a526eb48c

Author: amoralej

openstackclient/tests/unit/common/test_parseractions.py

@@ -92,7 +92,7 @@ def test_good_values(self):
             {'req1': 'aaa', 'req2': 'bbb'},
             {'req1': '', 'req2': ''},
         ]
-        self.assertItemsEqual(expect, actual)
+        self.assertCountEqual(expect, actual)
 
     def test_empty_required_optional(self):
         self.parser.add_argument(
@@ -116,7 +116,7 @@ def test_empty_required_optional(self):
             {'req1': 'aaa', 'req2': 'bbb'},
             {'req1': '', 'req2': ''},
         ]
-        self.assertItemsEqual(expect, actual)
+        self.assertCountEqual(expect, actual)
 
     def test_error_values_with_comma(self):
         self.assertRaises(