MB-12268: Adding a debug log, when clusterConfig is updated

Change-Id: I0cbb70789f84bddc644bdc4ee59c1e86e1821220
Reviewed-on: http://review.couchbase.org/41746
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>