Fix flakiness in DefaultVhalImpl_test.

    // Clear existing events.

    mEventQueue.flush();

    std::this_thread::sleep_for(std::chrono::milliseconds(500));

    // There should be no new events generated.

    EXPECT_EQ((size_t)0, mEventQueue.flush().size());

    // Technically there should be no new events generated, however, there might still be one event

    // in the queue while we are stopping the generator.

    EXPECT_LE(mEventQueue.flush().size(), 1u);

}

std::string getTestFilePath(const char* filename) {