Update RHEL7 element since release

This patch updates the RHEL7 element to work
properly now that it has changed from beta to
release status.  It includes a repo update to
locate os-config rpms not in epel yet and an
update to the latest cloud image name.

Change-Id: I05607d62193c8f8fb1c1bece9872d456b19c5a08
Merge "Update RHEL7 element since release"