fw_lab_triage_helper: support arbitrary pools

BUG=None
TEST=Ran with default pool, and with a pool (-pool faft-test) known
to contain non chromeos1 DUTs (so as to exercise the filtering).

Change-Id: I3555e93f0c8a78ecfcb9954e77aba4681ae020a6
Reviewed-on: https://chromium-review.googlesource.com/1741611
Tested-by: Kevin Shelton <kmshelton@chromium.org>
Commit-Ready: Kevin Shelton <kmshelton@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Greg Edelston <gredelston@google.com>
1 file changed