MB-100: add logs for debug

Change-Id: I4dfe42c527a3f631c382561c748ccf4caffedc38
Reviewed-on: http://review.couchbase.org/24990
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>