chromeos: Point TMPDIR to /usr/local/tmp during VM/DUT tests.

vpython uses both HOME and TMPDIR as workspaces. Now that /tmp is
mounted with noexec, we need to point vpython to a tmp dir without that
restriction.

Bug: 990859
Change-Id: I17629676abb898923658a48862a909e99d4fac1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1735554Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684074}

build/chromeos/test_runner.py

@@ -62,12 +62,13 @@ class RemoteTest(object):
   BASIC_SHELL_SCRIPT = [
     '#!/bin/sh',
 
-    # /home is mounted with "noexec" in the device, but some of our tools
-    # and tests use the home dir as a workspace (eg: vpython downloads
-    # python binaries to ~/.vpython-root). /usr/local/tmp doesn't have this
-    # restriction, so change the location of the home dir for the
-    # duration of the test.
+    # /home and /tmp are mounted with "noexec" in the device, but some of our
+    # tools and tests use those dirs as a workspace (eg: vpython downloads
+    # python binaries to ~/.vpython-root and /tmp/vpython_bootstrap).
+    # /usr/local/tmp doesn't have this restriction, so change the location of
+    # the home and temp dirs for the duration of the test.
     'export HOME=/usr/local/tmp',
+    'export TMPDIR=/usr/local/tmp',
   ]
 
   def __init__(self, args, unknown_args):