[U-Boot] [PATCH] test/py: Fix exception, do not parametrize with empty set

[Stephen Warren]

On 10/16/2016 12:17 PM, Stefan Brüns wrote:
> If the parameter set is empty, the pytest setup fails:
> ---
>     call: <CallInfo when='setup' exception: got empty parameter set
>     ['env__dfu_config'], function test_dfu at [...]test_dfu.py:107>
> ---
>
> This aborts pytest_runtest_makereport and later leads to an exception
> during the report generation, as the call to log.start_section(...)
> is never executed:
> ---
>     Exception: Block nesting mismatch:
>     "test_dfu[env__usb_dev_port0-env__dfu_config0]" ""
> ---

This patch causes failures with pytest 2.5 when env__dfu_configs is an 
empty list or not set at all. I've created an alternative patch that 
seems to work with both pytest 2.5 and 3, which I'll send in a minute.