This makes make-disk-image.nix slightly more consistent with other image
builders we have. Unfortunately I duplicated some code in doing so, but
this is temporary duplication on the path to consolidating everything.
See https://github.com/NixOS/nixpkgs/issues/23052 for more details on that.
I'm also exposing the option in the amazon-image.nix maintainer module.
We now generate a qcow2 image to prevent hitting Hydra's output size
limit. Also updated /root/user-data -> /etc/ec2-metadata/user-data.
http://hydra.nixos.org/build/33843133
The EBS and S3 (instance-store) AMIs are now created from the same
image. HVM instance-store AMIs are also generated.
Disk image generation has been factored out into a function
(nixos/lib/make-disk-image.nix) that can be used to build other kinds
of images.
