Setup periodic runs of ``run_all.sh``, which runs playbooks against
bridge.o.o and all hosts.

**Role Variables**

.. zuul:rolevar:: update_cron_interval

   .. zuul:rolevar:: minute
      :default: 15

   .. zuul:rolevar:: hour
      :default: *

   .. zuul:rolevar:: day
      :default: *

   .. zuul:rolevar:: month
      :default: *

   .. zuul:rolevar:: weekday
      :default: *

   .. zuul:rolevar:: ansible_cron_disable_job
      :default: false

      Disabled installed cron job.  This is only useful for CI jobs
      testing bridge.o.o so that the test host does not randomly run
      the script during CI tests that fall during the interval.