jobs/default: Add a variable indicating if we are targetting production
requested to merge anlambert/swh-jenkins-jobs:detect-production-jenkins-and-adapt-jobs-conf into master
Add production_jenkins global variable indicating if we are generating jobs
for production Jenkins based on the value of the current hostname.
It enables to remove or add some settings when generating jobs for a local jenkins server used for testing.
Use this new feature to remove cron triggers for jobs when not targetting production Jenkins.
Related to !176 (merged).