RDS parameter groups now create_before_destroy

This requires a change in name for each (using `name_prefix`), which
will likely recreate all parameter groups.  This is intended to work
around an issue where AWS won't allow the parameter group to be
recreated while RDS are using it.

See these issues for reference:

* hashicorp/terraform-provider-aws#6448
* hashicorp/terraform-provider-aws#6049
* hashicorp/terraform-provider-aws#2402
* hashicorp/terraform-provider-aws#1571
* hashicorp/terraform-provider-aws#526

ci/terraform/rds_module/parameter_group.tf

@@ -1,6 +1,6 @@
 resource "aws_db_parameter_group" "parameter_group_postgres" {
   count = "${var.rds_db_engine == "postgres" ? 1 : 0}"
-  name = "${var.rds_parameter_group_name != "" ?
+  name_prefix = "${var.rds_parameter_group_name != "" ?
     var.rds_parameter_group_name :
     "${replace("${var.stack_description}-${var.rds_db_name}", "/[^a-zA-Z-]+/", "-")}"}"
   family = "${var.rds_parameter_group_family}"
@@ -30,11 +30,15 @@ resource "aws_db_parameter_group" "parameter_group_postgres" {
     value = "${var.rds_force_ssl}"
     apply_method = "pending-reboot"
   }
+
+  lifecycle {
+    create_before_destroy = true
+  }
 }
 
 resource "aws_db_parameter_group" "parameter_group_mysql" {
   count = "${var.rds_db_engine == "mysql" ? 1 : 0}"
-  name = "${var.rds_parameter_group_name != "" ?
+  name_prefix = "${var.rds_parameter_group_name != "" ?
     var.rds_parameter_group_name :
     "${replace("${var.stack_description}-${var.rds_db_name}", "/[^a-zA-Z-]+/", "-")}"}"
   family = "${var.rds_parameter_group_family}"
@@ -46,4 +50,8 @@ resource "aws_db_parameter_group" "parameter_group_mysql" {
     name = "log_output"
     value = "FILE"
   }
+
+  lifecycle {
+    create_before_destroy = true
+  }
 }