nixos/taskserver: Set allowedTCPPorts accordingly

As suggested by @matthiasbeyer:

"We might add a short note that this port has to be opened in the
firewall, or is this done by the service automatically?"

This commit now adds the listenPort to
networking.firewall.allowedTCPPorts as soon as the listenHost is not
"localhost".

In addition to that, this is now also documented in the listenHost
option declaration and I have removed disabling of the firewall from the
VM test.

Signed-off-by: aszlig <[e-mail]>

nixos/modules/services/misc/taskserver/default.nix

···
       listenHost = mkOption {
         type = types.str;
         default = "localhost";
+        example = "::";
         description = ''
           The address (IPv4, IPv6 or DNS) to listen on.
+
+          If the value is something else than <literal>localhost</literal> the
+          port defined by <option>listenPort</option> is automatically added to
+          <option>networking.firewall.allowedTCPPorts</option>.
         '';
       };
 
···
           chmod go+x "${cfg.dataDir}/keys"
         '';
       };
+    })
+    (mkIf (cfg.listenHost != "localhost") {
+      networking.firewall.allowedTCPPorts = [ cfg.listenPort ];
     })
     { meta.doc = ./taskserver.xml; }
   ];

nixos/tests/taskserver.nix

···
 
   nodes = rec {
     server = {
-      networking.firewall.enable = false;
       services.taskserver.enable = true;
       services.taskserver.listenHost = "::";
       services.taskserver.fqdn = "server";
···
     };
 
     client1 = { pkgs, ... }: {
-      networking.firewall.enable = false;
       environment.systemPackages = [ pkgs.taskwarrior pkgs.gnutls ];
       users.users.alice.isNormalUser = true;
       users.users.bob.isNormalUser = true;