RDO QSG: Fix the broken link to an older version of epel

The repo configuration section was referring to epel 7.2 when the
current release is 7.5. That was making the rpm retrieval fail.
Placing the new rpm url (and using yum because it's nice) should
fix it.

Change-Id: Ice3f1724f88d9f65a39ff1ef0e4d7550d1b13e9a
Signed-off-by: Jan Hilberath <jan@midokura.com>
Merge "RDO QSG: Fix the broken link to an older version of epel"