added cron cookbook

    Description of your patch
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This cookbook allows user to easily configure cron jobs in an attributes file.

    Recommended Release Notes
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Adds a cron cookbook that automates the installation of cron jobs based on the attributes in the cookbook.
    
    Estimated risk
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None

    Components involved
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Cron

    Description of testing done
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Booted up a cluster containing a utility instance called 'cron', uncommented `require_recipe "cron"` from the main cookbook recipe, upload and applied then verified that the two test crons were installed.

    QA Instructions
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1) Boot up a cluster containing a utility instance called 'cron'
2) In cookbooks/main/recipes/default.rb, remove the comment from line 54
3) Upload/apply cookbooks to cluster
4) SSH into utility instance named cron and run 'crontab -e -u deploy'.  You should see two crons that echo test1 and test2