(RE-1648) Update EL 7 Mock Configs for RHEL 7 RC

This update reflects the changes to repo structure in the RHEL7
release cadidate that came out in 4/14. We're still using the
EL7 bandaid structure since the final repo paths aren't formalized
yet. This will be updated when the final paths are determined
(be they CentOS or RHEL 7).