Leave rhel, epel repos intact

Jinja templates will update the repo file if it does not match.
There is no need to remove the yum repo.  rdo-release and puppet
are put down from the rdo-release rpm and should be removed in a
packstack role

Change-Id: I6d2cfd88de069e5ced4ff175bbb9f176cf0d5885
Only add optional repo manually when distro != 7.0

When distro version is RHEL 7, do not try to manually add the optional
repo, as it will come from subman.

Simplify the epel repository placement. Use the same template for RHEL
6 and 7, and select the url based on that inside the template.

Change-Id: Ibefe7ece5f318987c05e17506170b2677742de2b