Using correct format of exceptions from JSON based APIs.

Also factoring out Py2/Py3 behavior as _generate_faux_mime_message().
H/T to @tseaver for the factoring out.

gcloud/exceptions.py

@@ -179,11 +179,11 @@ def make_exception(response, content, use_json=True):
         if use_json:
             payload = json.loads(content)
         else:
-            payload = {'message': content}
+            payload = {'error': {'message': content}}
     else:
         payload = content
 
-    message = payload.get('message', '')
+    message = payload.get('error', {}).get('message', '')
     errors = payload.get('error', {}).get('errors', ())
 
     try:

gcloud/storage/batch.py

@@ -167,9 +167,11 @@ def __exit__(self, exc_type, exc_val, exc_tb):
             _BATCHES.pop()
 
 
-def _unpack_batch_response(response, content):
-    """Convert response, content -> [(status, reason, payload)]."""
-    parser = Parser()
+def _generate_faux_mime_message(parser, response, content):
+    """Convert response, content -> (multipart) email.message.
+
+    Helper for _unpack_batch_response.
+    """
     # We coerce to bytes to get consitent concat across
     # Py2 and Py3. Percent formatting is insufficient since
     # it includes the b in Py3.
@@ -186,9 +188,15 @@ def _unpack_batch_response(response, content):
     ])
 
     if six.PY2:
-        message = parser.parsestr(faux_message)
+        return parser.parsestr(faux_message)
     else:  # pragma: NO COVER  Python3
-        message = parser.parsestr(faux_message.decode('utf-8'))
+        return parser.parsestr(faux_message.decode('utf-8'))
+
+
+def _unpack_batch_response(response, content):
+    """Convert response, content -> [(status, reason, payload)]."""
+    parser = Parser()
+    message = _generate_faux_mime_message(parser, response, content)
 
     if not isinstance(message._payload, list):
         raise ValueError('Bad response:  not multi-part')

gcloud/test_exceptions.py

@@ -55,7 +55,7 @@ def _callFUT(self, response, content):
     def test_hit_w_content_as_str(self):
         from gcloud.exceptions import NotFound
         response = _Response(404)
-        content = b'{"message": "Not Found"}'
+        content = b'{"error": {"message": "Not Found"}}'
         exception = self._callFUT(response, content)
         self.assertTrue(isinstance(exception, NotFound))
         self.assertEqual(exception.message, 'Not Found')
@@ -71,7 +71,7 @@ def test_miss_w_content_as_dict(self):
             'reason': 'test',
             }
         response = _Response(600)
-        content = {"message": "Unknown Error", "error": {"errors": [ERROR]}}
+        content = {"error": {"message": "Unknown Error", "errors": [ERROR]}}
         exception = self._callFUT(response, content)
         self.assertTrue(isinstance(exception, GCloudError))
         self.assertEqual(exception.message, 'Unknown Error')