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: I4c5451afece8dfff30aa1ec4c7e0d5eb277043fd
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

lower-constraints.txt

@@ -16,7 +16,6 @@ iso8601==0.1.11
 keystoneauth1==3.4.0
 linecache2==1.0.0
 mccabe==0.2.1
-mock==2.0.0
 netaddr==0.7.18
 netifaces==0.10.4
 os-client-config==1.28.0

oslo_utils/tests/test_eventletutils.py

@@ -13,11 +13,11 @@
 #    under the License.
 
 import threading
+from unittest import mock
 import warnings
 
 import eventlet
 from eventlet import greenthread
-import mock
 from oslotest import base as test_base
 import six
 

oslo_utils/tests/test_excutils.py

@@ -13,9 +13,9 @@
 #    under the License.
 
 import logging
+from unittest import mock
 
 import fixtures
-import mock
 from oslotest import base as test_base
 
 from oslo_utils import excutils

oslo_utils/tests/test_fnmatch.py

@@ -16,8 +16,8 @@ import fnmatch as standard_fnmatch
 import ntpath
 import posixpath
 import sys
+from unittest import mock
 
-import mock
 from oslotest import base
 import six
 

oslo_utils/tests/test_netutils.py

@@ -15,8 +15,8 @@
 
 import contextlib
 import socket
+from unittest import mock
 
-import mock
 import netifaces
 from oslotest import base as test_base
 import six

oslo_utils/tests/test_strutils.py

@@ -18,9 +18,9 @@
 import collections
 import copy
 import math
+from unittest import mock
 
 import ddt
-import mock
 from oslotest import base as test_base
 import six
 import testscenarios

oslo_utils/tests/test_timeutils.py

@@ -17,9 +17,9 @@ import calendar
 import datetime
 import logging
 import time
+from unittest import mock
 
 import iso8601
-import mock
 from oslotest import base as test_base
 from testtools import matchers
 

oslo_utils/tests/tests_encodeutils.py

@@ -15,7 +15,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
+from unittest import mock
+
 from oslo_i18n import fixture as oslo_i18n_fixture
 from oslotest import base as test_base
 import six

test-requirements.txt

@@ -17,9 +17,6 @@ stestr>=2.0.0 # Apache-2.0
 #  deps = {[testenv]deps} coverage
 coverage!=4.4,>=4.0 # Apache-2.0
 
-# mocking framework
-mock>=2.0.0 # BSD
-
 # used for oslotest cross-testing scripts
 oslo.config>=5.2.0 # Apache-2.0