devel/py-pytest: Update to 2.8.5

• Update PORTVERSION and distinfo checksum (2.8.5)
• Add USES zip accordingly (no tar.gz @ PyPI)
• Add pytest-xdist to TEST_DEPENDS
• Add NO_ARCH
• Remove TESTS option and OPTIONS helpers
• Update test target to new convention

Changes:

https://github.com/pytest-dev/pytest/blob/2.8.5/CHANGELOG