Koji Fedora28 Support Update

Koji Fedora28 support has been added, and appears to be working.

Here’s a scratch build I did testing it out http://koji.katello.org/koji/taskinfo?taskID=114708

We ended up adding a new builder to koji, and created a new ‘fedora’ channel for fedora builds (currently only fedora28).

Please let me know if you run into any issues