MB-8787 Account for worker_batch_size parameter too.

Change-Id: If22de82cbe3254680def894ff2fdd7c26cd40634
Reviewed-on: http://review.couchbase.org/28174
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>