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: I597461bc2ce6a480ea18950ded606ef7db717f2d
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
 netaddr==0.7.18
 openstackdocstheme==1.18.1

oslo_i18n/tests/test_factory.py

@@ -14,7 +14,8 @@
 #    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_i18n/tests/test_gettextutils.py

@@ -16,9 +16,9 @@
 
 import gettext
 import logging
+from unittest import mock
 
 from babel import localedata
-import mock
 from oslotest import base as test_base
 import six
 

oslo_i18n/tests/test_handler.py

@@ -15,8 +15,8 @@
 #    under the License.
 
 import logging
+from unittest import mock
 
-import mock
 from oslotest import base as test_base
 import six
 

oslo_i18n/tests/test_logging.py

@@ -14,7 +14,8 @@
 #    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_i18n import _factory

oslo_i18n/tests/test_message.py

@@ -17,9 +17,9 @@
 from __future__ import unicode_literals
 
 import logging
+from unittest import mock
 import warnings
 
-import mock
 from oslotest import base as test_base
 import six
 import testtools

oslo_i18n/tests/test_public_api.py

@@ -9,12 +9,10 @@
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
 #    under the License.
-"""A few tests that use the public API to ensure the imports work.
-"""
+"""A few tests that use the public API to ensure the imports work."""
 
 import unittest
-
-import mock
+from unittest import mock
 
 import oslo_i18n
 from oslo_i18n import _lazy

oslo_i18n/tests/test_translate.py

@@ -16,7 +16,8 @@
 
 from __future__ import unicode_literals
 
-import mock
+from unittest import mock
+
 from oslotest import base as test_base
 
 from oslo_i18n import _message

test-requirements.txt

@@ -4,7 +4,6 @@
 hacking>=3.0,<3.1.0 # Apache-2.0
 stestr>=2.0.0 # Apache-2.0
 
-mock>=2.0.0 # BSD
 oslotest>=3.2.0 # Apache-2.0
 coverage!=4.4,>=4.0 # Apache-2.0
 testscenarios>=0.4 # Apache-2.0/BSD