Allow selecting which IP to use to SSH into the cluster

[rpsene]

By default we are using the public IP to SSH into the cluster. This covers the case where we assume someone is running this automation from a remote source, outside PowerVS. Eventually someone will have a full deployment only within PowerVS using private IPs, without using any route outside this environment.

I would be a good feature if we can select via TF which IP we want to use: bastion_public_ip or bastion_private_ip.