add "standard" module, which includes flashimage kexec & jffs2

most systems need most of these, so it makes writing the docs a
lot easier

tests/min-copy-closure/configuration.nix

@@ -13,8 +13,6 @@ let
 in {
   imports = [
     ../../vanilla-configuration.nix
-    ../../modules/squashfs.nix
-    ../../modules/jffs2.nix
   ];
   config =  {
     services.sshd = longrun {