openshift.ks - add "EXTRA" repo vars for testing

enterprise bug 1119419
https://bugzilla.redhat.com/show_bug.cgi?id=1119419

This adds options for setting up additional repos for jbosseap,
jbossews, rhscl and rhel so we can test alpha/beta packages for channels
we depend on.
Copied and pasted from the code above, which AFAICT was introduced with be7ef6dc059ae51b1ab19f320df52a55a2215694

I certainly don't care. :)