Comment 3 for bug 1724623

Attached is a possible patch to remedy some of the issues (and a few other bugs i've seen in the backlog with errors re: EC2 and other clouds). the gist:

1. change how we check if something is a cloud-image, generally
2. use /etc/cloud/build.info as a check if something is a Canonical cloud image
   2a. if it's rolled by someone else, hard to guarantee things
3. use /run/cloud-init/instance-data.json as a local store of info
   3a. this will run on most supported clouds, and provide more info

I've tried to make some graceful warning prints and error catches, along the lines of "if it's not there, just move on."