MB-100: better logging in wait_till_total_numbers_match

Change-Id: I4a6ac70605bdf43430488a57a7a27203a07c4ed1
Reviewed-on: http://review.couchbase.org/23791
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>