Fix packer json creation

Previously this code had a hack in which it would get the packer config
as a string and then lazily echo that into a remote file. This should
be done with a local temporary directory and a put instead. Oh and make
the json look pretty while we are at it.
Update .gitignore

Make sure that our git status remains clean after a build
Add proper hooks for SIGINT cleanup

This does not implement cleanup yet, but it will in the future. This
change provides to hooks to get us there.
Change name from imagecreator to darkroom

The previous name was pretty terrible, so shippig this with a much
better name now.