add tests for delivery rate (h2o/h2o#2832)
add tests for delivery rate (h2o/h2o#2832)

cwyang/h2o,yannick/h2o,h2o/h2o,h2o/h2o,devnexen/h2o,cwyang/h2o,h2o/h2o,yannick/h2o,cwyang/h2o,yannick/h2o,h2o/h2o,devnexen/h2o,devnexen/h2o,yannick/h2o,yannick/h2o,yannick/h2o,yannick/h2o,h2o/h2o,h2o/h2o,devnexen/h2o,h2o/h2o,cwyang/h2o,devnexen/h2o,yannick/h2o,yannick/h2o,h2o/h2o,devnexen/h2o,devnexen/h2o,h2o/h2o,cwyang/h2o,devnexen/h2o,cwyang/h2o,cwyang/h2o,cwyang/h2o,devnexen/h2o