Since Ocata, it has been recommended to disable EPEL when using RDO
because of breaking backward compatibility.
https://docs.openstack.org/ocata/install-guide-rdo/environment-packages.html
There seems to be no special reason to use EPEL in case of RHEL.
Change-Id: Iadc351dac518c03163811aab4dfeee7ad0457687
Signed-off-by: Minho Ban <mhban@samsung.com>