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.

Change-Id: I1851a3b6a3efd96f632db16a1a8e6ea23a1feda0
Merge "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."