[PATCH] run-tests: forward Python USER_BASE from site (issue5425)

[Augie Fackler]

# HG changeset patch
# User Augie Fackler <augie at google.com>
# Date 1478812044 18000
#      Thu Nov 10 16:07:24 2016 -0500
# Node ID 4a82a34d2694953ad58e5565a318d6909978d4ca
# Parent  61c9f8b3663cc6144446bbe1b8d8fc5088f081be
run-tests: forward Python USER_BASE from site (issue5425)

We do this so that any linters installed via pip install --user don't
break. See https://docs.python.org/2/library/site.html#site.USER_BASE
for a description of what this nonsense is all about.

An alternative would be to not set HOME, but that'll cause other
problems (see issue2707), or to forward every single path entry from
sys.path in PYTHONPATH (which seems sketchy in its own way).

diff --git a/tests/run-tests.py b/tests/run-tests.py
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -58,6 +58,7 @@ import signal
 import socket
 import subprocess
 import sys
+import sysconfig
 import tempfile
 import threading
 import time
@@ -818,6 +819,7 @@ class Test(unittest.TestCase):
             offset = '' if i == 0 else '%s' % i
             env["HGPORT%s" % offset] = '%s' % (self._startport + i)
         env = os.environ.copy()
+        env['PYTHONUSERBASE'] = sysconfig.get_config_var('userbase')
         env['TESTTMP'] = self._testtmp
         env['HOME'] = self._testtmp
         # This number should match portneeded in _getport