Reapply "vm-state: fix and improve testing"

This reverts commit 99092f6e76.

vm-state: revert sysusers, improve testing

zerotier: enable persistence

vm-state: cleanup tests

nixosModules/clanCore/zerotier/default.nix

@@ -220,7 +220,7 @@ in
             --network-id "$facts/zerotier-network-id"
         '';
       };
-      # clanCore.state.zerotier.folders = [ "/var/lib/zerotier-one" ];
+      clanCore.state.zerotier.folders = [ "/var/lib/zerotier-one" ];
 
       environment.systemPackages = [ config.clanCore.clanPkgs.zerotier-members ];
     })