Usage

Place role call to meta/main.yml:

dependencies:
  - { role: cron, cron_tasks: "{{backups_mysql_cron_tasks}}" }

Or you can include role as task from Ansible 2.2:

- name: Add cron tasks
  include_role:
    name: cron
  vars:
    cron_tasks: "{{backups_mysql_cron_tasks}}"

Manage /etc/crontab

You can delete system /etc/crontab.
Attention, detecting just by "system-wide crontab" comment, may delete your manual tasks!
Enable owerwrite: cron_crontab_tasks_overwrite: yes, then define cron_crontab_vars and cron_crontab_tasks.