Stop using deprecated 'message' attribute in Exception

The 'message' attribute has been deprecated and removed
from Python3.
For more details, please check:
https://www.python.org/dev/peps/pep-0352/

Change-Id: I6b5596d2376a4013754471ce834e2ac651e377ba

nova/tests/unit/test_api_validation.py

@@ -275,10 +275,10 @@ class QueryParamsSchemaTestCase(test.NoDBTestCase):
                                req)
         if six.PY3:
             self.assertEqual("Invalid input for query parameters foo. Value: "
-                             "abc. 'abc' is not a 'uuid'", ex.message)
+                             "abc. 'abc' is not a 'uuid'", six.text_type(ex))
         else:
             self.assertEqual("Invalid input for query parameters foo. Value: "
-                             "abc. u'abc' is not a 'uuid'", ex.message)
+                             "abc. u'abc' is not a 'uuid'", six.text_type(ex))
 
     def test_validate_request_with_multiple_values(self):
         req = fakes.HTTPRequest.blank("/tests?foos=abc")

nova/tests/unit/volume/test_cinder.py

@@ -18,6 +18,7 @@ from cinderclient import exceptions as cinder_exception
 from keystoneclient import exceptions as keystone_exception
 import mock
 from oslo_utils import timeutils
+import six
 
 import nova.conf
 from nova import context
@@ -412,7 +413,7 @@ class CinderApiTestCase(test.NoDBTestCase):
                                attachment_id)
 
         self.assertEqual(404, ex.code)
-        self.assertIn(attachment_id, ex.message)
+        self.assertIn(attachment_id, six.text_type(ex))
 
     @mock.patch('nova.volume.cinder.cinderclient',
                 side_effect=exception.CinderAPIVersionNotAvailable(