Allow certbot wrapper to work when no argument is provided after the command

Summary: Fixes T1640.

Test Plan:
Tested on docker-001:

$ certbot renew
Saving debug log to /var/log/letsencrypt/letsencrypt.log
[...]

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1640

Differential Revision: https://devcentral.nasqueron.org/D2375