Use unittest.mock instead of third party mock

Now that we no longer support py27, we can use the standard library
unittest.mock module instead of the third party mock lib.

Change-Id: Ib1f840f0cb778219f7640a2ca307847a090de6aa
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

lower-constraints.txt

@@ -19,7 +19,6 @@ keystoneauth1==3.4.0
 linecache2==1.0.0
 MarkupSafe==1.0
 mccabe==0.2.1
-mock==2.0.0
 mox3==0.20.0
 msgpack-python==0.4.0
 netaddr==0.7.18

oslo_policy/tests/test_checks.py

@@ -13,7 +13,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
+from unittest import mock
+
 from oslotest import base as test_base
 
 from oslo_policy import _checks

oslo_policy/tests/test_external.py

@@ -14,7 +14,8 @@
 #    under the License.
 
 import json
-import mock
+from unittest import mock
+
 from oslo_serialization import jsonutils
 from requests_mock.contrib import fixture as rm_fixture
 import six.moves.urllib.parse as urlparse

oslo_policy/tests/test_generator.py

@@ -10,9 +10,9 @@
 #    under the License.
 
 import operator
+from unittest import mock
 import warnings
 
-import mock
 from oslo_config import cfg
 import stevedore
 import testtools

oslo_policy/tests/test_parser.py

@@ -13,7 +13,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
+from unittest import mock
+
 from oslotest import base as test_base
 import six
 

oslo_policy/tests/test_policy.py

@@ -16,8 +16,8 @@
 """Test of Policy Engine"""
 
 import os
+from unittest import mock
 
-import mock
 from oslo_config import cfg
 from oslo_context import context
 from oslo_serialization import jsonutils

oslo_policy/tests/test_shell.py

@@ -14,7 +14,8 @@
 #    under the License.
 
 import copy
-import mock
+from unittest import mock
+
 from oslo_serialization import jsonutils
 
 from oslo_policy import shell

oslo_policy/tests/test_sphinxpolicygen.py

@@ -10,7 +10,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
+from unittest import mock
+
 from oslotest import base
 
 from oslo_policy import sphinxpolicygen