VOL-1506: Change alarm error message to debug as a non-existent
managed entity instance is common when a new alarm is
raised

Change-Id: Ie6396443867d4274739623e55906153cfe25bab0
diff --git a/voltha/extensions/omci/database/alarm_db_ext.py b/voltha/extensions/omci/database/alarm_db_ext.py
index 2af6923..841e328 100644
--- a/voltha/extensions/omci/database/alarm_db_ext.py
+++ b/voltha/extensions/omci/database/alarm_db_ext.py
@@ -264,7 +264,7 @@
 
         except KeyError:
             if not create:
-                self.log.error('instance-proxy-does-not-exist', device_id=device_id,
+                self.log.debug('instance-proxy-does-not-exist', device_id=device_id,
                                class_id=class_id, instance_id=instance_id)
                 raise