Support EPEL for RHEL-7
Support EPEL for RHEL-7

This patch makes EPEL repo installation work on all RHEL versions.
EPEL release is not hardcoded anymore.

Change-Id: Ic2a776e563e1e0538806c5d6632e6a4f946be513

imcsk8/packstack,stackforge/packstack,stackforge/packstack,imcsk8/packstack,fr34k8/packstack,palmer159/openstack-test,fr34k8/packstack,stackforge/packstack,openstack/packstack,xbezdick/packstack,fr34k8/packstack,palmer159/openstack-test,openstack/packstack,mahak/packstack,openstack/packstack,imcsk8/packstack,mahak/packstack,xbezdick/packstack,palmer159/openstack-test,xbezdick/packstack,mahak/packstack