Move all of NixOS to nixos/ in preparation of the repository merge

nixos/modules/profiles/headless.nix

@@ -0,0 +1,21 @@
+# Common configuration for headless machines (e.g., Amazon EC2
+# instances).
+
+{ config, pkgs, ... }:
+
+with pkgs.lib;
+
+{
+  sound.enable = false;
+  boot.vesa = false;
+
+  # Don't start a tty on the serial consoles.
+  systemd.services."serial-getty@ttyS0".enable = false;
+  systemd.services."serial-getty@hvc0".enable = false;
+
+  # Since we can't manually respond to a panic, just reboot.
+  boot.kernelParams = [ "panic=1" "boot.panic_on_fail" ];
+
+  # Don't allow emergency mode, because we don't have a console.
+  systemd.enableEmergencyMode = false;
+}