valgrind: exclude bar_bad/bar_bad_xml from ptests

valgrind: exclude bar_bad/bar_bad_xml from ptests

The tests' output is non-deterministic and sometimes
doesn't match the sample output. This has been reported at
https://bugs.kde.org/show_bug.cgi?id=430321
(see also an earlier related bug https://bugs.kde.org/show_bug.cgi?id=358213)

Until upstream figures out how to fix this, let's not run the tests.

Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>