Partial fix for cron.present broken on SmartOS

This fixes part of my issue in #10959 where cron.present couldn't add more than a single job. So far, I've only tested this on develop, but my problem came down to the fact that the cron jobs were being created with the same default identifier, and then the cron code thought they were the same job.

I haven't tested it on other platforms, but it is possible this bug is affecting them as well since this is not a SmartOS specific codepath.