Override the default RHEL releasever

RHEL versions default releasever includes the minor versions or
6Server or 7Server. we need to override this to get epel-release
installed.
Before adding this, I checked whether other repo files use this variable and it turned out that none of them use it. so found it was safe.
Anyways will remove this file. Need to take a look as to when exactly we should be removing it.