[CentOS-mirror] Let's Encrypt certs for CentOS mirrors

Hi All,

Still haven’t heard back about whether it’s ok to use SSL on our mirror. If it is, it looks like ours might be once of the first to do so? Not seeing any mirrors wth https: https://www.centos.org/download/mirrors/

At any rate, if this ok to do, it would be great if all mirrors started adopting https on their public CentOS mirror. Certbot makes it incredibly easy to deploy a free Let’s Encrypt cert on your mirror, and it literally only takes about 30 seconds to run this nifty tool. https://certbot.eff.org

- Ryan