Showing a better config error message
Showing a better config error message

Previously we just showed a message saying that config was not defined. This
shows a better error message that can help developers fix the problem. Also,
the error message can be overriden.

daviddavis/runcible,jlsherrill/runcible,cfouant/runcible,Katello/runcible,cfouant/runcible,daviddavis/runcible,jlsherrill/runcible,Katello/runcible