Move getent.rb to lib/facter for puppet to autoload; Replace @ with _at_ for key tags

The getent facts were not being loaded from the lib/puppet/facts directory. So I moved the file to lib/facter.
Also, the tags for the keys use the name of the key. This prevented the use of an @ symbol in the name of the key. For all tags referring to keys, the @ is replaced with _at_.