MB-11952 Lower the default max number of readers.

Change-Id: I43dbcc4d606eea07276327ec7b9ed4f9bf3fc0e4
Reviewed-on: http://review.couchbase.org/40579
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>