Lists status of instances.

def list(ctx, scenario_name, format):  # pragma: no cover
    """ Lists status of instances. """
    args = ctx.obj.get('args')
    subcommand = base._get_subcommand(__name__)
    command_args = {
        'subcommand': subcommand,
        'format': format,
    }

    statuses = []
    s = scenarios.Scenarios(
        base.get_configs(args, command_args), scenario_name)
    for scenario in s:
        statuses.extend(base.execute_subcommand(scenario.config, subcommand))

    headers = [util.title(name) for name in status.get_status()._fields]
    if format == 'simple' or format == 'plain':
        table_format = 'simple'
        if format == 'plain':
            headers = []
            table_format = format
        _print_tabulate_data(headers, statuses, table_format)
    else:
        _print_yaml_data(headers, statuses)