tests: Make scan test cases more robust by allowing retries

tests: Make scan test cases more robust by allowing retries

These test caases depended on a single active scan round finding the AP.
It is possible for the Probe Response frame to get delayed sufficiently
to miss the response especially when testing under heavy load with
multiple parallel VMs. Allow couple of scan retries to avoid reporting
failures from these test cases.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>