VOL-943: Fix for event publish loop dropping subscribers

Change-Id: I96ca0a5bf0b06ee12140966dbfb0a15290e130df
diff --git a/common/event_bus.py b/common/event_bus.py
index 8c903d9..e717c16 100644
--- a/common/event_bus.py
+++ b/common/event_bus.py
@@ -91,6 +91,7 @@
         :param msg: Arbitrary python data as message
         :return: None
         """
+        from copy import copy
 
         def passes(msg, predicate):
             try:
@@ -105,7 +106,8 @@
         subscribers.extend(s for s in self.subscriptions.get(None, [])
                            if s.topic.match(topic))
 
-        for candidate in subscribers:
+        # iterate over a shallow-copy of subscribers
+        for candidate in copy(subscribers):
             predicate = candidate.predicate
             if predicate is None or passes(msg, predicate):
                 try: