Add a test framework for various wpa_supplicant failure cases

Add a test framework for various wpa_supplicant failure cases

For CONFIG_TESTING_OPTIONS=y builds, add a new test parameter than can
be used to trigger various error cases within wpa_supplicant operations
to make it easier to test error path processing. "SET test_failure
<val>" is used to set which operation fails. For now, 0 = no failures
and 1 = scan trigger fails with EBUSY. More operations can be added in
the future to extend coverage.

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