support/testing/tests/package/test_python_unittest_xml_reporting.py: fix flake8 warnings

Fixes:

support/testing/tests/package/test_python_unittest_xml_reporting.py:3:1: F401 'time' imported but unused
1     F401 'time' imported but unused
make: *** [Makefile:1220: check-flake8] Error 123

Signed-off-by: Pierre-Jean Texier <texier.pj2@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>