Fix ClientException init when there is no message on py34

BaseException.message was removed in python 3 per PEP 0352 so if no
message is passed to the ClientException __init__ it will blow up:

AttributeError: type object 'ClientException' has no attribute 'message'

So this change does two things:

1. Default to 'n/a' for message and details when body['keys'] doesn't
   have a message or details in it (which should be fine since
   from_response defaults to n/a if 'keys' is not in body).
2. Use getattr for self.__class__.message and default to None if that
   attribute is not set.  Arguably we could just remove this and make
   the message kwarg default to 'n/a' in ClientException.__init__ but
   I figured that was more invasive.

Closes-Bug: #1481478

Change-Id: I738cb9c8d4f015048c45a1df16bf18e29190e392

cinderclient/exceptions.py

@@ -82,7 +82,9 @@ class ClientException(Exception):
     """
     def __init__(self, code, message=None, details=None, request_id=None):
         self.code = code
-        self.message = message or self.__class__.message
+        # NOTE(mriedem): Use getattr on self.__class__.message since
+        # BaseException.message was dropped in python 3, see PEP 0352.
+        self.message = message or getattr(self.__class__, 'message', None)
         self.details = details
         self.request_id = request_id
 
@@ -176,8 +178,8 @@ def from_response(response, body):
         details = "n/a"
         if hasattr(body, 'keys'):
             error = body[list(body)[0]]
-            message = error.get('message', None)
-            details = error.get('details', None)
+            message = error.get('message', message)
+            details = error.get('details', details)
         return cls(code=response.status_code, message=message, details=details,
                    request_id=request_id)
     else:

cinderclient/tests/unit/test_exceptions.py

@@ -0,0 +1,32 @@
+# Copyright 2015 IBM Corp.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+"""Tests the cinderclient.exceptions module."""
+
+import requests
+
+from cinderclient import exceptions
+from cinderclient.tests.unit import utils
+
+
+class ExceptionsTest(utils.TestCase):
+
+    def test_from_response_no_body_message(self):
+        # Tests that we get ClientException back since we don't have 500 mapped
+        response = requests.Response()
+        response.status_code = 500
+        body = {'keys': ({})}
+        ex = exceptions.from_response(response, body)
+        self.assertIs(exceptions.ClientException, type(ex))
+        self.assertEqual('n/a', ex.message)