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

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.

enterprise #cherry-pick
enterprise card 237
https://trello.com/c/No7fswfn/237-5-confirm-rhscl-1-2-compatibility

Conflicts:
	enterprise/install-scripts/amazon/openshift-amz.sh
	enterprise/install-scripts/generic/openshift.sh
	enterprise/install-scripts/openshift.ks