autotest: Refactor logic to access iw link values into iw_runner

This lets us easily reuse this logic.

BUG=chromium:325924
TEST=wifi_matfunc still passes.

Change-Id: Iaa18e16645733952a5192b90cda565120be85e11
Reviewed-on: https://chromium-review.googlesource.com/179374
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
Tested-by: Christopher Wiley <wiley@chromium.org>
8 files changed