Use docker and aws

This builds upon Dyball's initial work (in #27) and cleans things up considerably.
I like to add some more explicit logging here so we get output to `STDOUT`, `syslog` and `/var/log/user-data.log`:

    exec > >(tee /var/log/user-data.log|logger -t user-data -s 2>/dev/console) 2>&1