several cron related test cases in LTP reveals that our current cron recipe
is not complete:

a) a complete cron hierarchy better have:
     /etc/crontab
     /etc/cron.d
     /etc/cron.hourly
     /etc/cron.daily
     /etc/cron.weekly
     /etc/cron.monthly

b) for a normal user to use crontab command:
     add a new group - crontab
     /usr/bin/crontab is setgid to root:crontab
     /var/spool/cron is owned by root:crontab

below are optional, and thus not included in the default setup:
     /etc/cron.deny
     /etc/cron.allow

cronie by default only allows root user to use crontab, if neither cron.deny
nor cron.allow exists. They are controlled by final policy deployed on the
product.