nix: add controller-host-entry.nix

Previously, a user not using the testing modules had to set the hosts
entry himself, while with the new module we get an error if that
controller host is not configured.

On-behalf-of: SAP stefan.kober@sap.com

Author: hertrste

modules/generic/controller-host-entry.nix

@@ -0,0 +1,19 @@
+{ lib, config, ... }:
+with lib;
+{
+  options.openstack = {
+    controllerIP = mkOption {
+      type = types.str;
+      description = ''
+        IP address of the controller. Will be used to make a /etc/hosts entry
+        to make the controller available via "controller".
+      '';
+    };
+  };
+
+  config = {
+    networking.extraHosts = ''
+      ${config.openstack.controllerIP} controller controller.local
+    '';
+  };
+}