Change in how security_groups is provided [rds module]

To avoid issues with Terraform not being able to compute the value of count (e.g. * module.rds_database.aws_security_group_rule.rds_sg_in: aws_security_group_rule.rds_sg_in: value of 'count' cannot be computed), you now have to provide the number of security groups provided in the security_groups variable, via the security_groups_count variable.

If the security groups you're providing to the rds module are already created, and you're fetching them from a data source or have them hard-coded, you could still use the length function to compute the value of security_groups_count, like:

variable "security_groups" {
  default = ["sg-12345676", "sg-9876543"]
}

module "rds" {
  source = "..."
  ...
  security_groups = "${var.security_groups}"
  security_groups_count = "${length(var.security_groups)}"
}