refs #2972 - jsonp support [rpm]

The PR test might fail on the foreman change, I'm not sure it's working right now for core packages.

foreman scratch builds:
http://koji.katello.org/koji/taskinfo?taskID=199914 f19
http://koji.katello.org/koji/taskinfo?taskID=199916 el6
http://koji.katello.org/koji/taskinfo?taskID=199917 el7

rack-jsonp scratch builds:
http://koji.katello.org/koji/taskinfo?taskID=199920
http://koji.katello.org/koji/taskinfo?taskID=199921
http://koji.katello.org/koji/taskinfo?taskID=199922

More explanation in the commit message as to why I had to change so much just to add jsonp.rb.