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: Iee2ca363966243826134c1b5f5c9762d4b53662f
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

muranopkgcheck/tests/test_error.py

@@ -12,7 +12,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
+from unittest import mock
 
 from muranopkgcheck import error
 from muranopkgcheck.tests import base

muranopkgcheck/tests/test_log.py

@@ -12,7 +12,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
+from unittest import mock
 
 from muranopkgcheck import log
 from muranopkgcheck.tests import base

muranopkgcheck/tests/test_manager.py

@@ -12,7 +12,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
+from unittest import mock
 
 from muranopkgcheck import error
 from muranopkgcheck import manager

muranopkgcheck/tests/test_manifest_validator.py

@@ -13,7 +13,7 @@
 #    under the License.
 
 
-import mock
+from unittest import mock
 
 from muranopkgcheck.tests import test_validator_helpers as helpers
 from muranopkgcheck.validators import manifest

muranopkgcheck/tests/test_muranopl_validator.py

@@ -13,7 +13,7 @@
 #    under the License.
 
 from copy import deepcopy
-import mock
+from unittest import mock
 
 from muranopkgcheck.tests import test_validator_helpers as helpers
 from muranopkgcheck.validators import muranopl

muranopkgcheck/tests/test_package.py

@@ -13,7 +13,7 @@
 #    under the License.
 
 
-import mock
+from unittest import mock
 
 from muranopkgcheck.tests import test_validator_helpers as helpers
 from muranopkgcheck.validators import package

muranopkgcheck/tests/test_pkg_loader.py

@@ -13,7 +13,7 @@
 #    under the License.
 
 from io import BytesIO
-import mock
+from unittest import mock
 import zipfile
 
 import yaml

muranopkgcheck/tests/test_plugin.py

@@ -12,7 +12,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
+from unittest import mock
 
 from muranopkgcheck import manager
 from muranopkgcheck import plugin

muranopkgcheck/tests/test_ui_validator.py

@@ -12,7 +12,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
+from unittest import mock
 
 from muranopkgcheck.tests import test_validator_helpers as helpers
 from muranopkgcheck.validators import ui

muranopkgcheck/tests/test_yaml_validator.py

@@ -12,8 +12,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
 import unittest
+from unittest import mock
 
 from muranopkgcheck.validators import base