Added availability_zone to root module (#40)

main.tf

@@ -64,6 +64,7 @@ module "db_instance" {
   db_subnet_group_name   = "${local.db_subnet_group_name}"
   parameter_group_name   = "${module.db_parameter_group.this_db_parameter_group_id}"
 
+  availability_zone   = "${var.availability_zone}"
   multi_az            = "${var.multi_az}"
   iops                = "${var.iops}"
   publicly_accessible = "${var.publicly_accessible}"

variables.tf

@@ -90,6 +90,11 @@ variable "db_subnet_group_name" {
 //  default     = ""
 //}
 
+variable "availability_zone" {
+  description = "The Availability Zone of the RDS instance"
+  default     = ""
+}
+
 variable "multi_az" {
   description = "Specifies if the RDS instance is multi-AZ"
   default     = false