[stable-2.13] Use unittest.mock instead of mock. (#77883)

This can only be done for controller tests.
(cherry picked from commit 3a9a23fb1a)

Co-authored-by: Matt Clay <matt@mystile.com>

test/units/executor/test_task_executor.py

@@ -19,10 +19,10 @@
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
-import mock
+from unittest import mock
 
 from units.compat import unittest
-from mock import patch, MagicMock
+from unittest.mock import patch, MagicMock
 from ansible.errors import AnsibleError
 from ansible.executor.task_executor import TaskExecutor, remove_omit
 from ansible.plugins.loader import action_loader, lookup_loader