Don't run sidekiq as root

The Sidekiq cookbook currently runs the Sidekiq server process as root. That's really not a good idea :weary: 

Unfortunately this won't be gracefully backwards compatible, since if you've used the cookbook previously, you'll have `sidekick_N.log` files in your app's `log` directory and the PID directory `/var/run/engineyard/sidekiq/appname` owned by root, which will need to change.