Use unittest.mock instead of third party mock

Now that we are py36 or later, we can use the standard library
unittest.mock module instead of the third party mock lib.

Change-Id: I9582d623727e5853637812083033a348b71551ce
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

designateclient/tests/test_utils.py

@@ -11,11 +11,9 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+from unittest import mock
 import uuid
 
-import mock
-
-
 from designateclient import exceptions
 from designateclient.tests import base
 from designateclient import utils

lower-constraints.txt

@@ -26,7 +26,6 @@ jsonschema==2.6.0
 keystoneauth1==3.4.0
 linecache2==1.0.0
 mccabe==0.2.1
-mock==2.0.0
 monotonic==0.6
 mox3==0.20.0
 msgpack-python==0.4.0

test-requirements.txt

@@ -4,7 +4,6 @@
 # Hacking already pins down pep8, pyflakes and flake8
 hacking>=1.1.0,<1.2.0 # Apache-2.0
 coverage!=4.4,>=4.0 # Apache-2.0
-mock>=2.0.0 # BSD
 oslo.config>=5.2.0 # Apache-2.0
 oslotest>=3.2.0 # Apache-2.0
 os-testr>=1.0.0 # Apache-2.0