In BrokerFacade figure out and catch specific Netconf Runtime Exceptions Instead of generic RuntimeException during merge operations.

While fixing the issue where a Netconf device was unable to handle empty list merges, we are catching the generic RuntimeException in BrokerFacace.java since there was no clarity on all possible exceptions thrown from the underlying broker. This fixes the issue but it is better to understand the exceptions thrown by NETCONF and catch specific exceptions. Alternatively we can make the NETCONF broker to throw specific exception during merge operations and catch it.
This bug is file for the purposes of refactoring this part of the code.