Doesn't handle timed-out cert requests

[kkuchta]

When running scarr deploy, you get to a step where it's waiting for dns records to get picked up by ACM so the new certificates can get validated. It says it's fine to quit scarr and come back later to try again. Apparently ACM cert provisioning requests time out after 72 hours, at which point you need to delete the request and try again.

1. Handle auto-deletion of existing acm requests

• possibly delete the previously-created dns validation records

2. Add some messaging like "Come back in a few (but no more than 72) hours" to that step.