patman: test_util: Fix printing results for failed tests

When printing a python tool's test results, the entire list of failed
tests and their tracebacks are reprinted for every failed test. This
makes the test output quite unreadable. Fix the loop to print failures
and tracebacks one at a time.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>