WIP: allow to run cronjob setup only on specified role/layer
Fix: syntax
Fix: FC021
Enhancement: spin off "deploy crontab" logic into library

 * add a few test cases to nail this
Fix: plz rubocop
Enhancement: avoid hard-coding
Fix: add missing attributes
Merge pull request #352 from till/topics/cronjob-deploy

WIP: allow to run cronjob setup only on specified role/layer