Remove usage of assert_called_once on Mock objects

mock 1.1.0 was released on 10 July 2015 which prevents users from using
non-existent assertion methods. This broke the test in the diff.

Co-Authored-By: Ian Cordasco <graffatcolmingov@gmail.com>
Closes-Bug: #1473454
Change-Id: I162b76bbd7d96c96787a8dd8f9642ca1c80c596a

glanceclient/tests/unit/v2/test_shell_v2.py

@@ -833,7 +833,7 @@ class ShellV2Test(testtools.TestCase):
 
             test_shell.do_md_resource_type_list(self.gc, args)
 
-            mocked_list.assert_called_once()
+            self.assertEqual(1, mocked_list.call_count)
 
     def test_do_md_namespace_resource_type_list(self):
         args = self._make_args({'namespace': 'MyNamespace'})

test-requirements.txt

@@ -5,7 +5,8 @@ hacking<0.11,>=0.10.0
 
 coverage>=3.6
 discover
-mock>=1.0
+mock>=1.0;python_version!='2.6'
+mock==1.0.1;python_version=='2.6'
 oslosphinx>=2.5.0 # Apache-2.0
 sphinx!=1.2.0,!=1.3b1,<1.3,>=1.1.2
 testrepository>=0.0.18