Backslashes escaping backslashes in cloud-init YAML as string in Elm is real ugly

!308 (comment 372880600)

We could

1. Put the whole shellUserData in a separate YAML file that is passed to Exosphere as a string flag at runtime in ports.js
2. Host the shell script parts of the user data as separate files that the instance downloads, verifies checksum of, and runs at first boot.

I believe this separation would make it all cleaner and remove most/all need for escaping.