'Builds up the path to a poster cache for a given Indexer ID
:param indexer_id: ID of the show to use in the file name
:return: a full path to the cached poster file for the given Indexer ID'

def poster_path(self, indexer_id):

    poster_file_name = (str(indexer_id) + u'.poster.jpg')
    return ek(os.path.join, self._cache_dir(), poster_file_name)
