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: I97af946c244559513689c1ea9ac2d736d55dbe0f
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

metalsmith/test/test_cmd.py

@@ -16,9 +16,9 @@
 import io
 import json
 import tempfile
+from unittest import mock
 
 import fixtures
-import mock
 import testtools
 
 from metalsmith import _cmd

metalsmith/test/test_instance.py

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import mock
+from unittest import mock
 
 from metalsmith import _instance
 from metalsmith.test import test_provisioner

metalsmith/test/test_instance_config.py

@@ -14,8 +14,8 @@
 # limitations under the License.
 
 import json
+from unittest import mock
 
-import mock
 import testtools
 
 from metalsmith import instance_config

metalsmith/test/test_provisioner.py

@@ -13,8 +13,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from unittest import mock
+
 import fixtures
-import mock
 from openstack import exceptions as os_exc
 import requests
 import testtools

metalsmith/test/test_scheduler.py

@@ -13,7 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import mock
+from unittest import mock
+
 import testtools
 
 from metalsmith import _scheduler

metalsmith/test/test_sources.py

@@ -13,7 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import mock
+from unittest import mock
+
 import testtools
 
 from metalsmith import exceptions

test-requirements.txt

@@ -6,7 +6,6 @@ doc8>=0.6.0 # Apache-2.0
 flake8-import-order>=0.13 # LGPLv3
 fixtures>=3.0.0 # Apache-2.0/BSD
 hacking>=3.0.0,<3.1.0 # Apache-2.0
-mock>=2.0 # BSD
 stestr>=1.0.0 # Apache-2.0
 testtools>=2.2.0 # MIT
 Pygments>=2.2.0 # BSD