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: Icd7019c924386fb9c047fc55fb98e45fcb79f2eb
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
 openstackdocstheme==1.20.0
 os-client-config==1.28.0

oslo_rootwrap/tests/test_functional.py

@@ -23,6 +23,7 @@ import signal
 import sys
 import threading
 import time
+from unittest import mock
 
 try:
     import eventlet
@@ -30,7 +31,6 @@ except ImportError:
     eventlet = None
 
 import fixtures
-import mock
 import six
 import testtools
 from testtools import content

oslo_rootwrap/tests/test_rootwrap.py

@@ -16,10 +16,10 @@ import logging
 import logging.handlers
 import os
 import tempfile
+from unittest import mock
 import uuid
 
 import fixtures
-import mock
 from six import moves
 import testtools
 

test-requirements.txt

@@ -11,10 +11,6 @@ stestr>=2.0.0 # Apache-2.0
 # this is required for the docs build jobs
 oslotest>=3.2.0 # Apache-2.0
 
-
-# mocking framework
-mock>=2.0.0 # BSD
-
 # rootwrap daemon's client should be verified to run in eventlet
 eventlet!=0.18.3,!=0.20.1,>=0.18.2 # MIT