fixes #3209 - exit code only zero by default

We also need to merge this

https://github.com/theforeman/kafo/pull/27

in kafo to make this work.

I hope it is now clear what I mean.

With this patch, you can run installer and by default you always get zero on
success. Although if you want to parse detailed puppet exit codes (0, 2 on
success), you can still provide extra option for that.