Occasional logging errors

They only happen sometimes, possibly in relation to running many tests in parallel.

--- Logging error ---
Traceback (most recent call last):
  File "/nix/store/55jafgppn0jfw38k6zayasnsby8x9dj5-python3-3.6.2/lib/python3.6/logging/__init__.py", line 995, in emit
    stream.write(self.terminator)
BlockingIOError: [Errno 11] write could not complete without blocking
Call stack:
  File "/home/vcunat/dev/resolver/tests/deckard/deckard.py", line 486, in <module>
    deckard()
  File "/home/vcunat/dev/resolver/tests/deckard/deckard.py", line 481, in deckard
    sys.exit(testset.run())
  File "/home/vcunat/dev/resolver/tests/deckard/pydnstest/test.py", line 27, in run
    self.log.info('[  OK  ] %s', name)
Message: '[  OK  ] %s'
Arguments: ('sets/resolver/world_cz_vutbr_www.rpl',)

or

[  OK  ] sets/resolver/val_nsec3_b5_wcnodata_nonc.rpl
--- Logging error ---
make[1]: *** [Makefile:48: sets/resolver/val_nsec3_b5_wcnodata_nonc.out] Error 120