allow load balancing mode to be set via env var
allow load balancing mode to be set via env var

matt-deboer/marathon-lb,knesenko/marathon-lb,JamesAwesome/marathon-lb,knesenko/marathon-lb,GrovoLearning/marathon-lb,mesosphere/marathon-lb,JamesAwesome/marathon-lb,GrovoLearning/marathon-lb,matt-deboer/marathon-lb,matt-deboer/marathon-lb,vixns/marathon-lb,mesosphere/marathon-lb,vixns/marathon-lb,vixns/marathon-lb,JamesAwesome/marathon-lb,knesenko/marathon-lb,GrovoLearning/marathon-lb,mesosphere/marathon-lb