This problem is caused by removal of psutil dependency from the git master branch while pypi is still not up to speed with the removal. Issue and PR to fix this have been created.
This bug only manifests itself when running certbot-auto from git, and temporary fix for the time being is to run:
git revert 9bd361b28d62a9c81695f0e2e4c7211fb70e5d66
on the local clone.