MB-11407: Add logs to the UPR consumer rollback code

On the UPR consumer side, there aren't enough logs to indicate
if a rollback has been processed or not.

Change-Id: I5df76097db803e4ed75915a92058f109f526dc16
Reviewed-on: http://review.couchbase.org/38456
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Sriram Ganesan <sriram@couchbase.com>