Automated the checking of unused DNS records

[afeld]

We should clean out records from this repository that aren't actually in use. Some ideas of things to check for:

• Public Route 53 zones where the domain isn't actually pointing to those nameservers
• A, AAAA, and CNAME records where that hostname doesn't respond

We should add a script to the repository to check for these things.

[adunkman]

Noticed continua11y.18f.gov is a 404 today:

dns/terraform/18f.gov.tf

Lines 395 to 401 in cb9c678

	resource "aws_route53_record" "18f_gov_continua11y_18f_gov_cname" {
	zone_id = "${aws_route53_zone.18f_gov_zone.zone_id}"
	name = "continua11y.18f.gov."
	type = "CNAME"
	ttl = 60
	records = ["dwz1sfldhro5q.cloudfront.net"]
	}

[lauraGgit]

@stvnrlly i believe that this was one of your projects - would you say that this makes sense to take out?

[afeld]

Closing as stale.