Add an after_script to cleanup job after generation and test

Goes together with an MR I'll create in jenkins-scripts.

This adds an after_script which looks for a file containing the oar job id, if found it oardels the job.

If the job "properly" succeeds or fails the file will be removed by the script in jenkins-scripts, if the job is cancelled the file will still be here and the after_script will take care of deleting the job.