fixes #7234 - add foreman-release-scl meta-package

Depends on the release RPMs from softwarecollections.org, for RHEL clone users
to get the repositories that provide RHSCL rebuilds.

extras/ will be consumed by the mash split script when we build repos, much
like comps/.  These files will be fetched and included into the finished repo.

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I've created an updated mash split script which seems to do the job, I created a test repo with the rhscl-* release packages inside from my packaging branch.

http://koji.katello.org/koji/taskinfo?taskID=163534 el6
http://koji.katello.org/koji/taskinfo?taskID=163535 el7