MB-100: Increase node fill threshold

Change-Id: I2d1ae272767a7d98afb501f6b8b9073b846bf14d
Reviewed-on: http://review.couchbase.org/28076
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>