MB-11864 Initialize max_workers variables before creating threads.

Change-Id: Ie7853d8bd874117e976c74708172a36cf8c8e7c0
Reviewed-on: http://review.couchbase.org/40156
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>