CPU microcode is not always prepended first in the initrd file

[lenzj]

Issue description

When enabling "hardware.cpu.intel.updateMicrocode = true;", the intel-ucode.img file is not always prepended first in the initrd file. If the "intel-ucode.img" file is not prepended first the system will crash at boot.

Steps to reproduce

Use the following two settings in the "configuration-hardware.nix" file (order doesn't matter):
boot.initrd.prepend = [ "/boot/crypto_keyfile.cpio.gz" ];
hardware.cpu.intel.updateMicrocode = true;

The order can be confirmed using the following command at the prompt:
nixos-option boot.initrd.prepend

Workaround

Place the following setting in the main "configuration.nix" file instead:
boot.initrd.prepend = [ "/boot/crypto_keyfile.cpio.gz" ];

Technical details

• System: (NixOS: 16.09.1650.d2cd8a0 (Flounder))
• Nix version: (nix-env (Nix) 1.11.6)
• Nixpkgs version: ("16.09.1650.d2cd8a0")