Disable zfs in the ISO for now

It's giving zpool-import.service errors.

http://hydra.nixos.org/build/16883184

nixos/modules/installer/cd-dvd/installation-cd-base.nix

@@ -43,7 +43,7 @@ with lib;
   boot.initrd.kernelModules = [ "fbcon" ];
 
   # Add support for cow filesystems and their utilities
-  boot.supportedFilesystems = [ "zfs" "btrfs" ];
+  boot.supportedFilesystems = [ /* "zfs" */ "btrfs" ];
 
   # Allow the user to log in as root without a password.
   users.extraUsers.root.initialHashedPassword = "";