adding conditional creation

## usage example

## required variables

`domain` - domain to create a zone for

## optional variables

`create_zone` - if we need to actually create said zone

## outputs

* `id` - The zone ID.

variable "zone" {}

variable "create_zone" {

  default = "false"

}

resource "cloudflare_zone" "dns_zone" {

  count = "${var.create_zone == "true" ? 1 : 0}"

  zone  = "${var.zone}"

}