text: Title: logging not captured with pytest 3.3 and xdist
  Body: Consider this file:
  
  ```python
  import logging
  logger = logging.getLogger(__name__)
  
  def test():
  	logger.warn('Some warning')
  ```
  
  When executing `pytest foo.py -n2`, the warning is printed to the console:
  
  ```
  ============================= test session starts =============================
  platform win32 -- Python 3.5.0, pytest-3.3.1, py-1.5.2, pluggy-0.6.0
  rootdir: C:\Users\bruno, inifile:
  plugins: xdist-1.20.1, forked-0.2
  gw0 [1] / gw1 [1]
  scheduling tests via LoadScheduling
  foo.py                       6 WARNING  Some warning
  .                                                                        [100%]
  ========================== 1 passed in 0.65 seconds ===========================
  ```
  
  Executing `pytest` normally without the `-n2` flags then the message is not printed.
  
  Using `pytest 3.3.1` and `xdist 1.20.1`.