Update gpg settings as requested in #497

This addresses the comments here: https://github.com/opscode/opscode-omnibus/issues/497

It's been run through CI here: http://wilson.ci.opscode.us/job/chef-server-12-trigger-ad_hoc/104/

Looking through the code it looks like this code gets executed as part of the server build so no further testing is needed.  Please validate that assumption while reviewing. :)