autotest: Move netperf_runner.py to server/cros/network

TEST=Ran wifi_rxampdu successfully.
BUG=chromium:258537

Change-Id: I5abebc9abdc4f2132a6145616d90f069257b16bb
Reviewed-on: https://gerrit.chromium.org/gerrit/61308
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
5 files changed