tests: Fix BSS table flushing and old result ignoring for WPS tests

tests: Fix BSS table flushing and old result ignoring for WPS tests

The WPS tests are more prone to fail if scan results from the previous
test cases are allowed to remain in the wpa_supplicant BSS table during
the consecutive test since the test setup uses the same BSSID for the
test APs that change their configuration. Avoid these mostly bogus
issues by enforcing wpa_supplicant to drop and ignore old scan results
during the WPS test cases.

Signed-hostap: Jouni Malinen <j@w1.fi>