Updated tasks to use ``systemctl`` for RHEL 7.

Updated tasks to use ``systemctl`` instead of ``service`` to manage
services as well as use OS-version specific service names (e.g.
``firewalld`` versus ``iptables``).

Also, cleaned up the ``cdn_install`` task by removing its ``subscribe``
and ``install_prerequisites`` calls since these already already handled
by ``product_install``.
I'm not sure what the intent is here, but this code is probably not doing what you intend. This might be what you intend:

    run('ping -c 1 -n $(hostname) | grep "icmp_seq"')

Or this might be what you intend:

    run('ping -c 1 -n {0} | grep "icmp_seq"'.format(proxy_info.hostname))