Fixes various issues in vSphere Terraform code (#8178)

* Fixes various issues in vSphere Terraform code

Provided to address various shortcomings and to fix the following
issue in upstream Kubespray:

https://github.com/kubernetes-sigs/kubespray/issues/8176

* Resolves Terraform formatting issues

* Sets default prefix to human-readable name

* Documents new default prefix in README

contrib/terraform/vsphere/modules/kubernetes-cluster/templates/cloud-init.tmpl

@@ -25,7 +25,7 @@ write_files:
           ens192:
             dhcp4: false #true to use dhcp
             addresses:
-            - ${ip}
+            - ${ip}/${netmask}
             gateway4: ${gw} # Set gw here
             nameservers:
               addresses: