Description
python 2.7 is EOL jan 1st 2020: https://github.com/python/devguide/pull/344
it's time, at least for 3.0+ to migrate the test execution framework to python 3.6.
this PR (https://github.com/apache/spark/pull/26330) does all of the above.
after 3.0 is cut, we can then add python3.8 and drop python2.7 and pypy2.5.1 test support.