Expand join definition to `join' call.

    :param join_definition: join definition
    :return: expanded join definition

def _expand_join(join_definition):
    """Expand join definition to `join' call.

    :param join_definition: join definition
    :return: expanded join definition
    """
    join_table_name = join_definition.pop('table')
    join_func = getattr(mosql_query, join_definition.pop('join_type', 'join'))
    return join_func(join_table_name, **join_definition)