nixos/vms: Fix LVM disk helper regression

Adding volume-group support changed the LVM disk helper's argument
meaning, so standard VM disks and the legacy darts calls resolved disk
names as volume groups.

Restore the main volume group for standard disks and map the differently
named darts volumes explicitly.

lib/default.nix

@@ -191,7 +191,7 @@ rec {
     };
     lvmDisk' = vg: lv: lvmDisk'' lv vg lv;
     lvmDisk = lvmDisk' "main";
-    disk = vm: lv: lvmDisk' lv "vm-${vm}-${lv}";
+    disk = vm: lv: lvmDisk'' lv "main" "vm-${vm}-${lv}";
   };
 
   deploy-rs =

nixos/boxes/colony/vms/default.nix

@@ -212,8 +212,8 @@
             cleanShutdown.timeout = 120;
             drives = [
               (mkMerge [ (vm.disk "darts" "root") { frontendOpts.bootindex = 0; } ])
-              (vm.lvmDisk' "media" "darts-media")
-              (vm.lvmDisk' "ext" "darts-ext")
+              (vm.lvmDisk'' "media" "main" "darts-media")
+              (vm.lvmDisk'' "ext" "main" "darts-ext")
             ];
           };
         };