Update aws tf (#5435)

* update aws tf to function as expected

* update tf version

* update syntax for tf v0.12

* update tf version in readme

* update per tf for v0.12

contrib/terraform/aws/README.md

@@ -10,7 +10,7 @@ This project will create:
 * AWS ELB in the Public Subnet for accessing the Kubernetes API from the internet
 
 **Requirements**
-- Terraform 0.8.7 or newer
+- Terraform 0.12.0 or newer
 
 **How to Use:**
 

contrib/terraform/aws/create-infrastructure.tf

 terraform {
-  required_version = ">= 0.8.7"
+  required_version = ">= 0.12.0"
 }
 
 provider "aws" {

contrib/terraform/aws/modules/elb/main.tf

@@ -28,7 +28,7 @@ resource "aws_security_group_rule" "aws-allow-api-egress" {
 # Create a new AWS ELB for K8S API
 resource "aws_elb" "aws-elb-api" {
   name            = "kubernetes-elb-${var.aws_cluster_name}"
-  subnets         = "${var.aws_subnet_ids_public}"
+  subnets         = var.aws_subnet_ids_public
   security_groups = ["${aws_security_group.aws-elb.id}"]
 
   listener {

contrib/terraform/aws/modules/vpc/outputs.tf

@@ -3,15 +3,15 @@ output "aws_vpc_id" {
 }
 
 output "aws_subnet_ids_private" {
-  value = ["${aws_subnet.cluster-vpc-subnets-private.*.id}"]
+  value = aws_subnet.cluster-vpc-subnets-private.*.id
 }
 
 output "aws_subnet_ids_public" {
-  value = ["${aws_subnet.cluster-vpc-subnets-public.*.id}"]
+  value = aws_subnet.cluster-vpc-subnets-public.*.id
 }
 
 output "aws_security_group" {
-  value = ["${aws_security_group.kubernetes.*.id}"]
+  value = aws_security_group.kubernetes.*.id
 }
 
 output "default_tags" {