nixos/gitlab: fixes

- fix timezone data not found
- fix module, add simple test
- allow to set port

nixos/tests/gitlab.nix

@@ -0,0 +1,19 @@
+# This test runs gitlab and checks if it works
+
+import ./make-test.nix {
+  name = "gitlab";
+
+  nodes = {
+    gitlab = { config, pkgs, ... }: {
+      virtualisation.memorySize = 768;
+      services.gitlab.enable = true;
+      services.gitlab.databasePassword = "gitlab";
+    };
+  };
+
+  testScript = ''
+    $gitlab->start();
+    $gitlab->waitForUnit("gitlab.service");
+    $gitlab->waitUntilSucceeds("curl http://localhost:8080");
+  '';
+}