MB-9457: pass swt low to child erlang

I.e. to spread all load to all cores quicker

Change-Id: I7940afa9f1e5a2796122926796490ca55808f4d0
Reviewed-on: http://review.couchbase.org/29994
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>