So it looks like we loose the ability to specify an arbitrary AMI ID with this change. I think that is still valuable to support (say I have my own AMI which has additional packages etc.). I guess you could check for the first character being 'v' and if not just use the given id ? 

Also it'll be good to have `latest` be a symlink in the github repo to 0.7.0 so the url resolution will work with latest too.