fix a bug that prevented JT admins from editing custom virtualenvs

see: https://github.com/ansible/tower/issues/1754

awx/api/views.py

@@ -404,9 +404,11 @@ class ApiV1ConfigView(APIView):
             data.update(dict(
                 project_base_dir = settings.PROJECTS_ROOT,
                 project_local_paths = Project.get_local_path_choices(),
-                custom_virtualenvs = get_custom_venv_choices(),
             ))
 
+        if JobTemplate.accessible_objects(request.user, 'admin_role').exists():
+            data['custom_virtualenvs'] = get_custom_venv_choices()
+
         return Response(data)
 
     def post(self, request):