Need ruby-shadow in order to set user passwords in Puppet

Without ruby-shadow, Puppet will fail to set user passwords and emit the following message:

   info: /User[mcfakey]: Provider useradd does not support features manages_passwords; not managing attribute password

See http://www.puppetcookbook.com/posts/managing-user-password-fails.html for more information.
Merge pull request #819 from theasci/master

Need ruby-shadow in order to set user passwords in Puppet