Release 7.8.3

Numerous fixes and updates including:

  + Support including forked Chef repositories.
  + Use a new chef cookbook for timezone handling (a fork of `rackspace_timezone`, which itself was a fork of `timezone-ii`).
  + Use a forked version of the `chef-sentry-handler` cookbook to report more information (OS, cookbook version).
  + Use the `yum` cookbook's default recipe to allow for configuration.
  + Clear `yum` metadata prior to adding repos (just to be safe).
  + Move the distro check to before package installation.

Besides, a few cleanup commits, and minor updates.