CHERRY-PICK: ethernet: implement link_only check to see if link is up

When link_only=True, the test only check if the iterface can be
found on DUT. We can also specify use_swconfig to use swconfig
command to check if link is up.

BUG=chrome-os-partner:34902
TEST=run ethernet test with link_only=True and iface set
TEST=run ethernet test with link_only=True and use_swconfig=True

Original-Change-Id: I6009e79c63e5da635e356f0509eb75a4c3767ae4
Reviewed-on: https://chromium-review.googlesource.com/241933
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Wei-Ning Huang <wnhuang@chromium.org>
Tested-by: Wei-Ning Huang <wnhuang@chromium.org>

Change-Id: I04a185d88977bda1667b97bfc529672ed6431c62
Reviewed-on: https://chromium-review.googlesource.com/245945
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Wei-Ning Huang <wnhuang@chromium.org>
Tested-by: Wei-Ning Huang <wnhuang@chromium.org>
1 file changed