nixos/alps: fix for Hydra failure

https://hydra.nixos.org/build/199758163

nixos/tests/alps.nix

@@ -90,7 +90,7 @@ import ./make-test-python.nix ({ pkgs, ... }: {
     };
   };
 
-  testScript = ''
+  testScript = { nodes, ... }: ''
     server.start()
     server.wait_for_unit("postfix.service")
     server.wait_for_unit("dovecot2.service")
@@ -99,6 +99,7 @@ import ./make-test-python.nix ({ pkgs, ... }: {
 
     client.start()
     client.wait_for_unit("alps.service")
+    client.wait_for_open_port(${toString nodes.client.config.services.alps.port})
     client.succeed("test-alps-login")
   '';
 })