Creating task with invalid property crashes in py3

Currently when you are trying to set invalid additional property for
task using py3 interpreter it will fail, because function `unicode` does
not exist in py3.

Fix it by replacing `unicode` with `utils.exception_to_str` which is
used in other modules already.

Change-Id: I5897868f801467a2eaa7585b5f2d578cef358426
Closes-Bug: 1439513

glanceclient/v2/tasks.py

@@ -110,7 +110,7 @@ class Controller(object):
             try:
                 setattr(task, key, value)
             except warlock.InvalidOperation as e:
-                raise TypeError(unicode(e))
+                raise TypeError(utils.exception_to_str(e))
 
         resp, body = self.http_client.post(url, data=task)
         #NOTE(flwang): remove 'self' for now until we have an elegant

tests/v2/test_tasks.py

@@ -187,6 +187,7 @@ schema_fixtures = {
                     'result': {},
                     'message': {},
                 },
+                'additionalProperties': False,
             }
         )
     }
@@ -275,3 +276,10 @@ class TestController(testtools.TestCase):
         task = self.controller.create(**properties)
         self.assertEqual(task.id, '3a4560a1-e585-443e-9b39-553b46ec92d1')
         self.assertEqual(task.type, 'import')
+
+    def test_create_task_invalid_property(self):
+        properties = {
+            'type': 'import',
+            'bad_prop': 'value',
+        }
+        self.assertRaises(TypeError, self.controller.create, **properties)