Increase timeout for slower builders.

Some of our slower builder (with latest_toolchain) are taking around
8 hours. This CL increases the timeout for such situations.

BUG=chromium:870916
TESTS=None

Change-Id: I8c15e4ecbd71f76bca65c6adcabd74df8da79660
Reviewed-on: https://chromium-review.googlesource.com/1167965


Commit-Ready: Luis Lozano <llozano@chromium.org>
Tested-by: Luis Lozano <llozano@chromium.org>
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>