publish extra tags/versions

From now on, we'll start respecting semversioning.

Removes need for call to check_old.sh

change at #7

The verification for out-of-sync branches was not removed. It's done transparently as part of the other scripts.

Fail scripts if AWS creds are missing

more context in #5

Pushes applied TF revision to S3

A file named tf-applied-revision.sha will be pushed to the same S3 bucket used for TF state files. This file will then be used to compare with the revision being built and resolve which layers where modified since then.