Use new EventHandlerBase API to simplify graceful stop logic

solvable/src/event_handler_main.py

@@ -165,10 +165,8 @@ def main():
         key='test'
     )
 
-    event_handlers = EventHandler.get_local_instances()
-    def stop(sig, frame):  # pylint: disable=unused-argument
-        for eh in event_handlers:
-            eh.stop()
+    def stop(*_): 
+        EventHandler.stop_all_instances()
         exit(0)
     signal(SIGTERM, stop)
     signal(SIGINT, stop)