Increase disk sink maximum buffer size.

Change-Id: Ia24e4b3b9c46517b4bd40d2920f9ef51166461ed
Reviewed-on: http://review.couchbase.org/38759
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
[ale] Don't use helper macro to specify supervisor children.

Change-Id: Ifd6919a3f4b7a9be0137cac01e11cc9ab14b11c9
Reviewed-on: http://review.couchbase.org/38760
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>