Freeze Break request: update mirrors.centos.org cert

[Kevin Fenzi]

We host the mirros.centos.org site on our proxies (redirecting to
mirrormanager). It has a letsencrypt cert and it expires on March 22nd. 

We have a new cert ready now, so I would like to just update it now so
it's all in sync. 

Will require pushing the new cert to the ansible-private repo and
running proxies playbook to deploy it. 

Can I get +1's for this from sysadmin-main/releng folks?

kevin