test.py: Add tst-threadcomplete.so to blacklist

The test hangs at times and while there's a fix brewing, it's making
'make check' less useful.

Lets add it back when it works all the time.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
test.py: Show blacklisted tests

Make blacklisted tests visible during test.py run to attract attention
to them and hopefully get them fixed:

  TEST tst-strerror_r.so         OK  (1.083 s)
  TEST tst-threadcomplete.so     SKIPPED
  TEST tst-tracepoint.so         OK  (1.120 s)

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>