To kill/abort all jobs that are in "waiting"-state, you will have to run the following curl-command;
curl -Haccept:text/plain -uadmin:$ADMINPASSWORD "localhost:8080/API/job;state=WAITING" | xargs -n1 sh -c 'curl -uadmin:$ADMINPASSWORD -X DELETE "localhost:8080/API/job/$0"'