h2olog: check if -t <arg> exists
h2olog: check if -t <arg> exists

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