[metastore] Provide the partition keys of a table in json
e.g.
$.post('http://127.0.0.1:8000/notebook/api/autocomplete/default/blog', {'snippet': hueDebug.ko.mapping.toJSON({'type': 'hive'})})
If partitions:
"{"status": 0, ... "partition_keys": [{"type": "string", "name": "dy"}, {"type": "string", "name": "dm"}, {"type": "string", "name": "dd"}, {"type": "string", "name": "dh"}]}"
If no partition:
partition_keys": []