* tests: refactor and cleanup
* refactor: more consistent
* tests: vendor six
* tests: more xfails, nicer system
* tests: simplify to info
* tests: suggestions from @YannickJadoul and @bstaletic
* tests: restore some pypy tests that now pass
* tests: rename info to env
* tests: strict False/True
* tests: drop explicit strict=True again
* tests: reduce minimum PyTest to 3.1
