Don't raise FileNotFoundError during disabling keepalived

In case when keepalived's config is not existing already, there is no
need to raise any exception while L3 agent is trying to clean this
config.

Change-Id: I9ec81ad0c10379294d3145c5902e8b81b65c0221
Closes-Bug: #1892866

neutron/agent/l3/ha_router.py

@@ -200,7 +200,10 @@ class HaRouter(router.RouterInfo):
             return
         self.keepalived_manager.disable()
         conf_dir = self.keepalived_manager.get_conf_dir()
-        shutil.rmtree(conf_dir)
+        try:
+            shutil.rmtree(conf_dir)
+        except FileNotFoundError:
+            pass
 
     def _get_keepalived_instance(self):
         return self.keepalived_manager.config.get_instance(self.ha_vr_id)