Return a list of VMs that are on the provider

def list_nodes(conn=None, call=None):
    '''
    Return a list of VMs that are on the provider
    '''
    if call == 'action':
        raise SaltCloudSystemExit(
            'The list_nodes function must be called with -f or --function.'
        )

    if not conn:
        conn = get_conn()

    ret = {}
    nodes = conn.list_servers()

    for node in nodes:
        public_ips = []
        private_ips = []
        ret = {}

        size = node.get('hardware').get('fixed_instance_size_id', 'Custom size')

        if node.get('private_networks'):
            for private_ip in node['private_networks']:
                private_ips.append(private_ip)

        if node.get('ips'):
            for public_ip in node['ips']:
                public_ips.append(public_ip['ip'])

        server = {
            'id': node['id'],
            'image': node['image']['id'],
            'size': size,
            'state': node['status']['state'],
            'private_ips': private_ips,
            'public_ips': public_ips
        }
        ret[node['name']] = server

    return ret