autotest: Move path utilities out of wifi_test_utils

Refactor the utilities to be usable from a client context.

BUG=None
TEST=network_WiFi_SimpleConnect.wifi_checkWPA_TKIP passes.

Change-Id: If820921d777b0377f529ea40cc34c3377e192150
Reviewed-on: https://chromium-review.googlesource.com/236658
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
Tested-by: Christopher Wiley <wiley@chromium.org>
6 files changed