[Nix-dev] luks changes

[Lluís Batlle i Rossell]

Hello people using luksRoot... I changed that a bit on nixos, I hope that for
the better. I used it to get a ciphered swap that works for hibernation.

If you had:
boot.initrd.luksRoot = "/dev/sda2";

Then now you have to write:
boot.initrd.luks.enable = true;
boot.initrd.luks.devices = [ { name = "luksroot"; device = "/dev/sda2"; } ]

Luckily nixos-rebuild will let you know about bad syntax before booting anything
broken.

I don't know if I could have written some kind of deprecated warning while
keeping the luksRoot syntax, as in rename.nix... I welcome suggestions.

Regards,
Lluís.