VOL-2535: onu-adapter crashing due to unhandled exception, err msg : key not found.
Added try, catch handling in pyvoltha

Change-Id: I3e7b6fe6dedecf2f526464529d1003c768fec960
diff --git a/VERSION b/VERSION
index b001d23..3a660ff 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.3.12
+2.3.13
diff --git a/pyvoltha/common/event_bus.py b/pyvoltha/common/event_bus.py
index 08c4595..05019aa 100644
--- a/pyvoltha/common/event_bus.py
+++ b/pyvoltha/common/event_bus.py
@@ -82,8 +82,11 @@
         :param subscription: subscription object as was returned by subscribe
         :return: None
         """
-        topic_key = self.subs_topic_map[subscription]
-        self.subscriptions[topic_key].remove(subscription)
+        try:
+           topic_key = self.subs_topic_map[subscription]
+           self.subscriptions[topic_key].remove(subscription)
+        except KeyError:
+           log.error('key not found', key=subscription)
 
     def publish(self, topic, msg):
         """