Create ILB firewall name with prefix "k8s-fw".
Create ILB firewall name with prefix "k8s-fw".

ExternalLB and the healthcheck firewall rules follow this naming
convention.
addressed review comments.

Kubernetes-commit: 0d0d7ec8e7b17237b4cbc8e97d1d990ddbfcbe68

kubernetes/legacy-cloud-providers