Add rubygem-bastion package

Alright, the final one in line. Scratches:

F19 http://koji.katello.org/koji/taskinfo?taskID=171319
EL6 http://koji.katello.org/koji/taskinfo?taskID=171320
EL7 http://koji.katello.org/koji/taskinfo?taskID=171321
~> 2.5.0