Support cloud-init

This image currently uses tiny-ec2-bootstrap which is a very minimal re-implementation of cloud-init functionality. As cloud-init support for Alpine begins to take shape, and to support #99 (closed), we should start to think about moving to cloud-init instead of tiny-ec2-bootstrap.

The original rationale for tiny-ec2-bootstrap was twofold: cloud-init is a complicated ball of mud and adding Alpine support was seriously non-trivial (and IMO not needed to support a single cloud provider like EC2), and the dependency graph for cloud-init pulls in a ton of additional dependencies which increase image size (significantly, relative to current image size, as I recall). The later is still likely the case but will have to be looked past to support #99 (closed). The former I think is being worked on in upstream.