Use unittest.mock instead of mock

The mock third party library was needed for mock support in py2
runtimes. Since we now only support py36 and later, we can use the
standard lib unittest.mock module instead.

Change-Id: I3be6c40ef61e0334cab860689abbee84f5d19265

Author: 4383

designateclient/tests/v2/test_nameservers.py

@@ -13,7 +13,7 @@
 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 # License for the specific language governing permissions and limitations
 # under the License.
-from mock import patch
+from unittest.mock import patch
 
 from designateclient.tests import v2
 from designateclient.v2 import zones

designateclient/tests/v2/test_recordsets.py

@@ -13,9 +13,9 @@
 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 # License for the specific language governing permissions and limitations
 # under the License.
+from unittest.mock import patch
 import uuid
 
-from mock import patch
 import testtools
 
 from designateclient import exceptions

designateclient/tests/v2/test_timeout.py

@@ -16,7 +16,7 @@
 
 from keystoneauth1.identity import generic
 from keystoneauth1 import session as keystone_session
-from mock import Mock
+from unittest.mock import Mock
 
 from designateclient.tests import v2
 from designateclient.v2.client import Client