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.
fixes #12912 - switch to CentOS SCLo SIG builds
Swaps dependencies for softwarecollections.org with the CentOS SCLo SIG
release packages, which are copied into our repo by the mash script when
listed in extras/ so non-CentOS users and those without CentOS Extras
enabled can install it.
The packages are better maintained and will allow us to depend on sclo-*
packages in future. Maintenance of softwarecollections.org builds seems
to have stopped in favour of the SCLo SIG.