frappy.has_changed() should not be triggered repeatedly

fix bug

devices.py

@@ -139,6 +139,7 @@ class FrappyConfig(Device):
     meanings.remove('nodes')
     _trigger_change = None
     _previous_shown = None
+    _previous_state = None
     _initial_config = None
     _servers_loaded = False
 
@@ -163,7 +164,8 @@ class FrappyConfig(Device):
             try:
                 cfgs = self.check_services()
                 changes, state, remarks = self.to_consider(cfgs)
-                if state != self._previous_shown and changes:
+                if state != self._previous_state and changes:
+                    self._previous_state = state
                     cmd = 'frappy.has_changed()  # inserted automatically when frappy or sea servers changed'
                     controller.new_request(ScriptRequest(cmd, None, User('guest', USER)))
             except RequestError as e:
@@ -338,7 +340,7 @@ class FrappyConfig(Device):
         controller = session.daemon_device._controller
         controller.block_requests(r['reqid'] for r in controller.get_queue()
                                   if r['script'].startswith('frappy.has_changed()'))
-        self._previous_shown = state
+        self._previous_state = self._previous_shown = state
         session.log.info(all_info(allcfg))
 
         if changes:
@@ -385,7 +387,8 @@ class FrappyConfig(Device):
             error, proposed, state, remarks = fm.get_server_state(config.instrument, cfgs)
             self._initial_config = proposed
             if not error:
-                self._previous_shown = state  # otherwise the server state will be shown on startup
+                # do not show server state on startup
+                self._previous_state = self._previous_shown = state
         return self._initial_config.get(service)
     
     def has_changed(self, show_server_state='auto'):
@@ -664,3 +667,6 @@ class FrappyNode(SecNodeDevice, Moveable):
         if (code, text) == (status.ERROR, 'reconnecting'):
             return '%s (frappy not running)' % result
         return '%s (%s)' % (result, text)
+
+    def doFinish(self):
+        return False  # avoid warning in finish() when target does not match