makeTestClan: simplify - move parameters into module

... in preparation of removing the makeTestClan wrapper and make this a module instead that can be imported into any test.

lib/test/container-test-driver/driver-module.nix

@@ -36,7 +36,7 @@ let
   machineNames = map (name: "${name}: Machine;") pythonizedNames;
   pythonizedNames = map pythonizeName nodeHostNames;
 in
-{
+lib.mkIf (config.clan.test.useContainers or true) {
   defaults.imports = [
     ./nixos-module.nix
   ];