Clean imports in code

In some part in the code we import objects. In the Openstack style guidelines
they recommend to import only modules. [1]: "Do not import objects, only modules".

[1] https://docs.openstack.org/hacking/0.10.3/

Change-Id: I90ae12639be39b72bac7907cbd71182f44dae02d

mistralclient/tests/unit/v2/test_cli_action_execs.py

@@ -18,7 +18,7 @@ import copy
 import json
 import sys
 
-from six import StringIO
+import six
 
 import mock
 
@@ -160,7 +160,7 @@ class TestCLIActionExecutions(base.BaseCommandTest):
 
         # Redirect the stderr so it doesn't show during tox
         _stderr = sys.stderr
-        sys.stderr = StringIO()
+        sys.stderr = six.StringIO()
 
         for state in states:
             self.assertRaises(

mistralclient/tests/unit/v2/test_cli_tasks.py

@@ -21,7 +21,6 @@ import mock
 
 from mistralclient.api.v2 import tasks
 from mistralclient.commands.v2 import tasks as task_cmd
-from mistralclient.commands.v2.tasks import TaskFormatter
 from mistralclient.tests.unit import base
 
 TASK_DICT = {
@@ -62,7 +61,7 @@ class TestCLITasksV2(base.BaseCommandTest):
         self.assertEqual([EXPECTED_TASK_RESULT], result[1])
         self.assertEqual(
             self.client.tasks.list.call_args[1]["fields"],
-            TaskFormatter.COLUMN_FIELD_NAMES
+            task_cmd.TaskFormatter.COLUMN_FIELD_NAMES
         )
 
     def test_list_with_workflow_execution(self):