Searchers for JSON files in this repo and returns
    a map of collection id ==> (`tag`, dir, collection filepath)
    where `tag` is typically the shard name

def create_id2collection_info(path, tag):
    """Searchers for JSON files in this repo and returns
    a map of collection id ==> (`tag`, dir, collection filepath)
    where `tag` is typically the shard name
    """
    d = {}
    for triple in os.walk(path):
        root, files = triple[0], triple[2]
        for filename in files:
            if filename.endswith('.json'):
                # trim file extension and prepend owner_id (from path)
                collection_id = "{u}/{n}".format(u=root.split('/')[-1], n=filename[:-5])
                d[collection_id] = (tag, root, os.path.join(root, filename))
    return d