Update notes for submitted changes

* Closes-Bug: #1349980 The issue is when we process rabbitmq message for instance ip delete, we access the virtual network. In case of the problem, the VN is deleted by this time. Hence the exception is thrown in "dbe_delete_notification" function of InstanceIpServer. Fix: 1. ip_free_notify should only free the ip from the subnet it already knows. 2. Even if the "dbe_xxx_notification" fails, inform the if map server.  This is to ensure that cassandra and if map are in sync. 3. Add logging for "dbe_oper_subscribe" exceptions. The error is critical and hard to debug without this error log.