security/py-{acme,certbot}: Update to 0.16.0

Common:

• Update PORTVERSION and distinfo checksum (0.16.0)

Changelog: https://github.com/certbot/certbot/blob/master/CHANGELOG.md#0160---2017-07-05

Reviewed by: koobs (maintainer, py-certbot)
Approved by: koobs (maintainer, py-certbot)
Differential Revision: https://reviews.freebsd.org/D11517