Catch all for serialization errors

Rather than odd bool error, return something a
bit more precise.

confluent_server/confluent/core.py

@@ -1051,6 +1051,8 @@ def dispatch_request(nodes, manager, element, configmanager, inputdata,
             rsp = exc.deserialize_exc(rsp)
         if isinstance(rsp, Exception):
             raise rsp
+        if not rsp:
+            raise Exception('Error in cross-collective serialize/deserialze, see remote logs')
         yield rsp