Switch to CentOS SCLorg SIG repository
Software collections are moving into the CentOS SCLorg/SCLo SIG as an upstream location, which somewhat replaces softwarecollections.org. We could configure the SCLo repository (e.g. http://mirror.centos.org/centos/7/sclo/) instead of scl.org from our "foreman-release-scl" RPM.
This will allow us to depend on SCLo collections such as the upcoming RoR 4.2 collection, and it's generally a little more structured than scl.org with a publicly available build system.