added attribute to manage jenkins arguments

- On RHEL, the template for /etc/sysconfig/jenkins doesn't have an
  attribute for the JENKINS_ARGS config. Added an attribute for that.
renaming attribute

- Rename the attribute to be consistent with the config option in the
  template.
forgot to rename attribute in template
Update job.rb

Ajout de securité pour passer la creation des jobs une fois jenkins sécurisé
Update metadata.rb
bugfix: update a job

- added a condition to authenticate the call made to jenkins' API to
  check if the job exists or not.