replace webob.Response with werkzeug Response

Replace webob usage in one more file. Document a TODO that should
be clarified, we should probably be using json_response rather than
Response() here.

Modify the TestMeddleware to not rely on the content_type attribute
being present, while werkzeug.wrappers Response() has it the BaseResponse()
object which is often returned in tests does not have it.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

mediagoblin/tests/tools.py

@@ -78,7 +78,7 @@ class TestingMeddleware(BaseMeddleware):
 
     def process_response(self, request, response):
         # All following tests should be for html only!
-        if response.content_type != "text/html":
+        if getattr(response, 'content_type', None) != "text/html":
             # Get out early
             return