[backend] Use new formatting for error string generation

beat/web/backend/views.py

@@ -53,8 +53,8 @@ def scheduler(request):
     response = scheduler_api(request)
 
     if response.status_code != 200:
-        messages.error(request, "Error contacting the scheduler at %s:%d " \
-                "[%s/%d] %s" % (settings.SCHEDULER_ADDRESS,
+        messages.error(request, "Error contacting the scheduler at {}:{} " \
+                "[{}/{}] {}".format(settings.SCHEDULER_ADDRESS,
                     settings.SCHEDULER_PORT, response.status_text,
                     response.status_code, response.data))
         return render_to_response('backend/scheduler.html', dict(),