Import opscode-cookbooks/cron version dce04363b6a02d36f8da88f202cedfae2daa6a2c
Make sure cron is on.  #2816.

Issue relationship: logrotate is run by cron, and we've got a
chef-client log rotation configuration, but (somehow) crond isn't
running on some of our nodes.  This change makes sure it's on.