Confmon: Log when a config is rejected due to no changes

This allows one to see that the library is indeed receiving a proper
config, but that the cluster has nothing new to report about it.

Change-Id: Ib2a258cd27a34fa259a833433824a474871031f8
Reviewed-on: http://review.couchbase.org/39752
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>