How to use the jumbo.core.clusters function in jumbo

def create(ctx, name, domain, template):
    """Create a new cluster.

    :param name: New cluster name
    """

    click.echo('Creating "%s"...' % name)
    try:
        clusters.create_cluster(cluster=name,
                                domain=domain,
                                template=template)
    except ex.CreationError as e:
        print_with_color(e.message, 'red')
    else:
        click.echo('Cluster "{}" created (domain name = "{}").'.format(
            name,
            domain if domain else '%s.local' % name))
        set_context(ctx, name)

def listclusters(full):
    """List clusters managed by Jumbo."""
    try:
        limit = 40
        if full:
            limit = 1000
        cluster_table = PrettyTable(['Name', 'Domain Name', 'VMs',
                                     'Services'])
        cluster_table.align['Name'] = 'l'
        cluster_table.align['Domain Name'] = 'l'
        cluster_table.align['Services'] = 'l'
        for cluster in clusters.list_clusters():
            cluster_table.add_row([cluster['cluster'],
                                   cluster['domain'],
                                   len(cluster['nodes']),
                                   '\n'.join(cluster['services'])])
    except ex.LoadError as e:
        print_with_color(e.message, 'red')
        if e.type == 'NoConfFile':
            click.echo('Use "repair" to regenerate "jumbo_config".')
    else:
        cluster_table.sortby = 'Name'
        click.echo(cluster_table)

def load_config(cluster):
    """Load a cluster in the session.

    :param cluster: Cluster name
    :type cluster: str
    :return: True on success
    """
    global svars

    if not checks.check_cluster(cluster):
        raise ex.LoadError('cluster', cluster, 'NotExist')

    if not clusters.check_config(cluster):
        raise ex.LoadError('cluster', cluster, 'NoConfFile')
    else:
        try:
            with open(JUMBODIR + cluster + '/jumbo_config', 'r') as jc:
                svars = json.load(jc)
        except IOError as e:
            raise ex.LoadError('cluster', cluster, e.strerror)

    vs.update_versions_file()

    return True