fix cloudstack eval, remove formats-broken

fixes the following eval error by defaulting to ext4.

error:
       Failed assertions:
       - Mountpoint '/': 'autoResize = true' is not supported for
       'fsType = "auto"'. fsType has to be explicitly set and
       only the following support it: ext3, ext4, btrfs, xfs.

README.md

@@ -47,7 +47,7 @@ format | description
 --- | ---
 amazon | Amazon EC2 image
 azure | Microsoft azure image (Generation 1 / VHD)
-~~cloudstack~~ | qcow2 image for cloudstack. This module is broken, PRs welcome.
+cloudstack | qcow2 image for cloudstack. 
 do | Digital Ocean image
 docker | Docker image (uses systemd to run, probably only works in podman)
 gce | Google Compute image

formats-broken/cloudstack.nix → formats/cloudstack.nix

@@ -9,6 +9,8 @@
     "${toString modulesPath}/virtualisation/cloudstack-config.nix"
   ];
 
+  fileSystems."/".fsType = lib.mkDefault "ext4";
+
   system.build.cloudstackImage = import "${toString modulesPath}/../lib/make-disk-image.nix" {
     inherit lib config pkgs;
     diskSize = 8192;