def cluster_ips(test_vars):
    """
    Return a list of known cluster IPs. The cluster mgmt IP, at a minimum,
    must be known. Cluster node and vserver IPs are also added to the list of
    cluster IPs that is returned.
    """
    c_ips = [test_vars["cluster_mgmt_ip"]]
    if "cluster_node_ips" in test_vars:
        c_ips += test_vars["cluster_node_ips"]
    if "cluster_vs_ips" in test_vars:
        c_ips += test_vars["cluster_vs_ips"]
    return c_ips