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: Ie775b99cdb645f072c0a22fa1a1a47448970b103
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

monasca_common/tests/policy/test_policy.py

@@ -14,8 +14,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
 import requests_mock
+from unittest import mock
 
 from oslo_context import context
 from oslo_policy import policy as os_policy

monasca_common/tests/test_confluent_kafka.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import mock
+from unittest import mock
 
 from monasca_common.confluent_kafka import consumer
 from monasca_common.confluent_kafka import producer

monasca_common/tests/test_kafka.py

@@ -10,7 +10,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-import mock
+from unittest import mock
 
 from oslotest import base
 

monasca_common/tests/test_repositories.py

@@ -10,7 +10,7 @@
 #   See the License for the specific language governing permissions and
 #   limitations under the License.
 
-import mock
+from unittest import mock
 
 from oslotest import base
 

monasca_common/tests/test_rest.py

@@ -10,7 +10,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-import mock
+from unittest import mock
 
 from oslotest import base
 

test-requirements.txt

@@ -8,7 +8,6 @@ Babel!=2.4.0,>=2.3.4 # BSD
 coverage!=4.4,>=4.0 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD
 httplib2>=0.9.1 # MIT
-mock>=2.0.0 # BSD
 oslo.context>=2.19.2 # Apache-2.0
 oslotest>=3.2.0 # Apache-2.0
 stestr>=1.0.0 # Apache-2.0