devel/lutok: update to 0.6.1

This version contains several enhancements described here in the release
notes:

• Version 0.6
• Version 0.6.1

Adjust the logic while here in some subtle ways:

• Only require ATF and package the tests if the port is built with the TEST option on.
• Switch from jmmv's GitHub repo to the freebsd GitHub repo.

Approved by: bofh (maintainer)
Reviewed by: bofh
Differential Revision: https://reviews.freebsd.org/D49568