provider/aws: Add db_param group to RDS Cluster Instance test

builtin/providers/aws/resource_aws_rds_cluster_instance_test.go

@@ -180,7 +180,22 @@ resource "aws_rds_cluster_instance" "cluster_instances" {
   identifier              = "tf-cluster-instance-%d"
   cluster_identifier      = "${aws_rds_cluster.default.id}"
   instance_class          = "db.r3.large"
+  db_parameter_group_name = "${aws_db_parameter_group.bar.name}"
 }
 
+resource "aws_db_parameter_group" "bar" {
+  name   = "tfcluster-test-group"
+  family = "aurora5.6"
+
+  parameter {
+    name         = "back_log"
+    value        = "32767"
+    apply_method = "pending-reboot"
+  }
+
+  tags {
+    foo = "bar"
+  }
+}
 `, n, n)
 }