re-roll /etc/cron.d/autocert hour/minute less frequently

[Paul Collins]

Every time write_cronjob is called, it re-renders /etc/cron.d/autocert with a new random minute and hour. If this happens often enough, it's possible (and has been observed in practice) that the cron job will not run for an extended period, leading to a nagios alert (best case) or expired certificate (worst case).

Per logs, this is the culprit:

@when('nrpe-external-master.available')
def configure_nagios(nagios):
    if hookenv.hook_name() == 'update-status':
        return
    # [...]
    write_cronjob()

From checking the Juju log it seems the breakdown of not-short-circuited hooks are:

    143 "leader-settings-changed"
     65 "leader-elected"
      1 "config-changed"
      1 "juju-info-relation-changed"