Add foreman_docker plugin + deps

foreman_docker:
https://rubygems.org/gems/foreman_docker
el6: http://koji.katello.org/koji/buildinfo?buildID=9823
f19: http://koji.katello.org/koji/buildinfo?buildID=9824

docker-api:
el6: http://koji.katello.org/koji/buildinfo?buildID=9821
f19: http://koji.katello.org/koji/buildinfo?buildID=9822

archive-tar-minitar:
el6: http://koji.katello.org/koji/buildinfo?buildID=9818
f19: https://apps.fedoraproject.org/packages/rubygem-archive-tar-minitar