Gitlab: Rework sjg-lab calling test.py to be closer to test.py stage

Gitlab: Rework sjg-lab calling test.py to be closer to test.py stage

There are a few differences between how the test.py stage invokes
test.py and how the sjg-lab stage invokes test.py. As a start of making
both the code and the output and artifacts similar, this updates the
sjg-lab stage with the following:
- Pass "-ra" so that we get the summary information in the job
- Make use of TEST_PY_EXTRA for passing "--capture=tee-sys"
- Re-order some of the arguments to be the same order when possible.

And most importantly:
- Create and save as an artifact the junitxml output.

The last part here is the kind of test result information that in the
future we should determine how to archive for future reference.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@konsulko.com>