Cleanup default value of cluster_virtual_ip

Currently cluster_virtual_ip having default value 55.55.55.55

On capo env, on workload cluster. It will always set display_external_ip as 55.55.55.55 which is wrong

Following discussion: https://sylva-projects.slack.com/archives/C04BQQANHA5/p1740555316177589

There needs to cleanup the IP and set as empty for default case