MB-8685: what's this message for Flush

[alk@tut.by: added ticket reference]

Change-Id: I9af2d72abef2962a6e28f56bc3649b278200ec7b
Reviewed-on: http://review.couchbase.org/40171
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>