autotest: WiFi: Add test for an AP changing security mode

Add a test that explicitly tests whether the DUT can connect to
an AP after it has changed security mode but not its SSID or
BSSID.

BUG=chromium:206299
TEST=Run test before and after upcoming fix

Change-Id: If6070df70baffe2e2b0fe4a15e7019631b7fbdc3
Reviewed-on: https://gerrit.chromium.org/gerrit/46440
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
2 files changed