change res of get_raw_stats from dict to list

when i invoke the web api of broker for `get_raw_stats` i get the error page saying that "dict doesn't have a method append". So, i think the auther may mean that the **res** variable in **brokerdaemon.py**'s **get_raw_stats** should be a list, since list has the method append. I have changed **res** to list and i finally get the correct output, something like "[{"module_name": "webui", "queue_size": 0}]"