autotest: Add autotest for wake on SSID

Add autotest to ensure that a DUT will wake up in dark resume on the appearance
of a whitelisted SSID.

Also:
- Add additional test statement in network_WiFi_WakeOnDisconnect and
  network_WiFi_WoWLAN to ensure that the NIC does not fully wake up when the
  wake trigger is received (DUT should only wake in dark resume).
- Shorten control file descriptions of wake on WiFi auto tests.
- Add docstrings in wifi_client.py to fix lint errors.

BUG=chromium:463296
TEST=Run network_WiFi_WakeOnSSID, network_WiFi_WakeOnDisconnect, and
     network_WiFi_WoWLAN using test_that on samus servo wificell.

Change-Id: I9e5a0d06f22ec8eda3e0d1e255ca789ae7338bce
Reviewed-on: https://chromium-review.googlesource.com/231451
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Samuel Tan <samueltan@chromium.org>
Commit-Queue: Samuel Tan <samueltan@chromium.org>
Tested-by: Samuel Tan <samueltan@chromium.org>
7 files changed