skip tasks if preinstalled

roles/jitsimeet/tasks/main.yml

@@ -9,6 +9,7 @@
   # import role webserver
   - import_role:
       name: webserver # required. The name of the role to be executed.
+    when: preinstalled == false or preinstalled is not defined
 
   # install software
   - include_tasks: prepare_system.yml