test_concurrent_futures now produces too much output on stderr.

$ ./python -m test test_concurrent_futures >/dev/null
Exception in initializer:
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/concurrent/futures/process.py", line 170, in _process_worker
    initializer(*initargs)
  File "/home/serhiy/py/cpython/Lib/test/test_concurrent_futures.py", line 66, in init_fail
    raise ValueError('error in initializer')
ValueError: error in initializer
Exception in initializer:
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/concurrent/futures/process.py", line 170, in _process_worker
    initializer(*initargs)
  File "/home/serhiy/py/cpython/Lib/test/test_concurrent_futures.py", line 66, in init_fail
    raise ValueError('error in initializer')
ValueError: error in initializer
...

What is worse, this output looks as errors report.