modules/microvm-host: let update-microvm handle more cases

modules/microvm-host.nix

@@ -89,9 +89,11 @@
 
             if [ -e booted ]; then
               nix store diff-closures $(readlink booted) $NEW
+            elif [ -e current ]; then
+              echo "NOT BOOTED! Diffing to old current:"
+              nix store diff-closures $(readlink current) $NEW
             else
-              echo "NOT BOOTED? Run:"
-              echo systemctl start microvm@$NAME
+              echo "NOT BOOTED?"
             fi
 
             CHANGED=no