This prevents seeing lots of warnings about missing hashes/sizes in the
database when running "nix-store --verify --check-contents" for the
first time.
(cherry picked from commit 64aed5e78f)
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.
(cherry picked from commit e018e10ba64e3277f11f4123bc46fc68def970dd)
