[swarming] Enforce test runner to use v8 base dir as cwd.

[swarming] Enforce test runner to use v8 base dir as cwd.

BUG=chromium:535160
LOG=n

Committed: https://crrev.com/41e0965c9ce47c19a013714e6ddbebe9d3421c42
Cr-Commit-Position: refs/heads/master@{#31308}

[Michael Achenbach, 2015-10-15 14:07:25]

machenbach@chromium.org changed reviewers:
+ jkummerow@chromium.org

[Michael Achenbach, 2015-10-15 14:08:44]

machenbach@chromium.org changed reviewers:
+ tandrii@chromium.org

[Michael Achenbach, 2015-10-15 14:08:45]

PTAL

[Michael Achenbach, 2015-10-15 14:09:17]

THis is to clean up errors like this:
http://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20swarming%20st...

[Michael Achenbach, 2015-10-15 14:09:58]

The CQ bit was checked by machenbach@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-10-15 14:10:10]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1397593004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1397593004/1

[Jakob Kummerow, 2015-10-15 14:25:49]

lgtm

[Michael Achenbach, 2015-10-15 14:26:22]

The CQ bit was unchecked by machenbach@chromium.org

[Michael Achenbach, 2015-10-15 14:26:27]

The CQ bit was checked by machenbach@chromium.org

[commit-bot: I haz the power, 2015-10-15 14:26:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1397593004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1397593004/1

[commit-bot: I haz the power, 2015-10-15 15:07:03]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-15 15:07:30]

Patchset 1 (id:??) landed as
https://crrev.com/41e0965c9ce47c19a013714e6ddbebe9d3421c42
Cr-Commit-Position: refs/heads/master@{#31308}