devel/py-tox: Update to 2.1.1

• Update PORTVERSION and distinfo checksum (2.1.1)
• Update COMMENT to match upstream (setup.py:description=)
• Update RUN_DEPENDS
• Add TEST_DEPENDS
• Rename test target since the framework supports TEST_DEPENDS et al.

Changes:

https://tox.readthedocs.org/en/latest/changelog.html