I propose to revert the change because test_datetime now takes up to 20 minutes, which causes random failures, especially on the slow "ARMv7 Ubuntu 3.x" buildbot:
http://bugs.python.org/issue30822#msg297734

This revert is part of the new policy to keep buildbots green:
https://mail.python.org/pipermail/python-committers/2017-June/004588.html

The revert is just a solution to get more time to fix a proper fix, before reapply the commit.