[Katello] katello-deploy updates

For those who use katello-deploy to spin up new environments, you can
now define custom boxes if you want more than one of a type (e.g. 2
centos7-devel boxes). This update also has the added benefit of
allowing the specification of installer options easily when using
katello-deploy. For more information see:

https://github.com/Katello/katello-deploy#adding-custom-boxes

Eric