Empty test suite is okay test suite.

Don't fail the rest of the test suites if one of them is empty.

Fixes: 6ebf5866 ("kunit: tool: add Python wrappers for running KUnit tests")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Tested-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>