Add test for set_config for NIDAQ device

The set_config method seems to be important for the device integration. I would propose to add a test to cover a few cases here. Since this is relatively closely linked to the backend, I would propose that @hitz_s or @clark_a adds this. I prepared a test method already with #TODO #20 (closed):

def test_set_config(mock_nidaq):
    dev = mock_nidaq
    # TODO #21 Add test logic for set_config, issue created #