Fixes #6272/BZ1118479 - move Bastion guide to katello.org.

Move Bastion documentation to katello.org. These links will
point to the github files themselves for now and will be
updated once the docs site is live.

http://projects.theforeman.org/issues/6272
https://bugzilla.redhat.com/show_bug.cgi?id=1118479