filesystems/py-libzfs: 2.0.0

Truenas has abandoned this project. I've made a personal fork and
applied various fixes there. Switch the port to point at my fork.

https://github.com/asomers/py-libzfs/blob/master/CHANGELOG.md

Sponsored by: ConnectWise
Reviewed by: arrowd
Approved by: ports (arrowd)
Differential Revision: https://reviews.freebsd.org/D57277