2020-02: tox ci broken on py27-macos and pypy

[ssbarnea]

Apparently tox own CI is broken on two places and this is a blocking issue for merning any other changes.

AFAIK I was not able to replicate any of these locally and I suspect they could even be flaky.

Both of them are on less-mainstream platforms which makes me think that they may not be considered as part of the merge criteria.

py27-macos

171250Z + [2]..._______________________\n0:01:41.707345   a: commands succeeded\n0:01:41.707401 ERROR:   b: parallel child exit code 2\n\n'
2020-02-12T14:38:10.2171360Z 	[<TracebackEntry /Users/runner/runners/2.164.8/work/1/s/tests/integration/test_parallel_interrupt.py:73>]
2020-02-12T14:38:10.2171430Z test_parallel_interrupt failed; it passed 0 out of the req

pypy-linux

_______________ TestConfigTestEnv.test_default_factors_conflict ________________

tests/unit/config/test_config.py:1948: Failed
E           Failed: DID NOT WARN. No warnings of type (<type 'exceptions.UserWarning'>,) was emitted. The list of emitted warnings is: [].

[ssbarnea]

Fixed by #1521