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: Ibd39328c27b68190e2edbf1f52fcea52db3ae791
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

lower-constraints.txt

@@ -43,7 +43,6 @@ kombu==4.0.0
 linecache2==1.0.0
 MarkupSafe==1.1.0
 mccabe==0.2.1
-mock==2.0.0
 monotonic==0.6
 mox3==0.20.0
 msgpack-python==0.4.0

openstackclient/tests/unit/identity/v3/test_access_rule.py

@@ -14,8 +14,8 @@
 #
 
 import copy
+from unittest import mock
 
-import mock
 from osc_lib import exceptions
 from osc_lib import utils
 

test-requirements.txt

@@ -5,7 +5,6 @@ hacking>=2.0.0 # Apache-2.0
 coverage!=4.4,>=4.0 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD
 flake8-import-order>=0.13 # LGPLv3
-mock>=2.0.0 # BSD
 oslotest>=3.2.0 # Apache-2.0
 requests>=2.14.2 # Apache-2.0
 requests-mock>=1.2.0 # Apache-2.0