mechanism for passing koji global options from obal

[komidore64]

The current way that foreman and katello use obal (with our koji instance) requires one to edit the koji config a certain way. It assumes that the base command koji defaults to the koji you're wanting to use, but what if you had your own koji config or had to interact with multiple build instances? Having the ability to call koji -c ~/.koji/my-special-config would be useful.