It tried creating directories multiple times without -p, so it failed.

Commits: https://github.com/pypa/virtualenv/compare/15.1.0...16.0.0
Changelog: https://virtualenv.pypa.io/en/latest/changes/#id1

Commits: https://github.com/pypa/setuptools/compare/v39.0.1...v39.1.0
Changelog:
https://github.com/pypa/setuptools/blob/v39.1.0/CHANGES.rst#v3910

Commits: https://github.com/tox-dev/tox/compare/2.9.1...3.0.0
Changelog: https://tox.readthedocs.io/en/latest/changelog.html#id4

Commits: https://github.com/pytest-dev/pytest/compare/3.2.2...3.5.1
Changelog:
https://github.com/pytest-dev/pytest/blob/3.5.1/CHANGELOG.rst#pytest-351-2018-04-23