[PATCH] run-tests: avoid set PYTHONUSERBASE environment variable to None

[Yuya Nishihara]

On Mon, 08 Jan 2018 13:23:13 +0000, Mihai Popescu wrote:
> # HG changeset patch
> # User Mihai Popescu <mihai at unity3d.com>
> # Date 1515415963 -3600
> #      Mon Jan 08 13:52:43 2018 +0100
> # Node ID 913c426a392121e6f629f591374b8a10d55c05ea
> # Parent  4c3a4bb31c0e3d9b8920b4c9b64ae930b1fe52ce
> run-tests: avoid set PYTHONUSERBASE environment variable to None

Queued for stable, thanks.