The latest release of Certbot and the acme library can use Python 3 [0].

These patches create a new python-mock@2 variable, and then upgrade
certbot and python-acme to use Python 3 by default. I did some light
testing by renewing some certificates.

[0]
https://github.com/certbot/certbot/pull/4568/commits/48b47274e7e6b11b7748b72a8e87add3f218e8b7