jenkins-job-cancel: improvements
jenkins-job-cancel: improvements

Adds the following improvements to the `jenkins-job-cancel`
script that can be called to abort running Jenkins jobs:
 - use `argparse` command line parameters for better usability
 - be more verbose when cancelling jobs
 - add the option to wait until cancelled jobs finishe executing

gosipyan/automation,SUSE-Cloud/automation,SUSE-Cloud/automation,aspiers/automation,gosipyan/automation,aspiers/automation,aspiers/automation,aspiers/automation,gosipyan/automation,SUSE-Cloud/automation,SUSE-Cloud/automation,gosipyan/automation