Attach child handler loop.

[heliomeiralins]

Fix problems reported in #238 for Python3.6. ( In python3.5 I couldn't reproduce the error)
Tested with python versions: 2.7.13, 3.4.5, 3.5.2 and 3.6.0.

In python 3.4, and 3.5, we have this:

Exception ignored in: <bound method _UnixSelectorEventLoop.__del__ of <_UnixSelectorEventLoop running=False closed=True debug=False>>
Traceback (most recent call last):
  File "/home/meiralins/.pyenv/versions/3.4.5/lib/python3.4/asyncio/base_events.py", line 417, in __del__
  File "/home/meiralins/.pyenv/versions/3.4.5/lib/python3.4/asyncio/unix_events.py", line 58, in close
  File "/home/meiralins/.pyenv/versions/3.4.5/lib/python3.4/asyncio/unix_events.py", line 139, in remove_signal_handler
TypeError: signal handler must be signal.SIG_IGN, signal.SIG_DFL, or a callable object
Exception ignored in: Exception ignored in: Exception ignored in: %

Exception ignored in: <bound method BaseEventLoop.__del__ of <_UnixSelectorEventLoop running=False closed=True debug=False>>
Traceback (most recent call last):
  File "/home/meiralins/.pyenv/versions/3.5.2/lib/python3.5/asyncio/base_events.py", line 431, in __del__
  File "/home/meiralins/.pyenv/versions/3.5.2/lib/python3.5/asyncio/unix_events.py", line 58, in close
  File "/home/meiralins/.pyenv/versions/3.5.2/lib/python3.5/asyncio/unix_events.py", line 139, in remove_signal_handler
  File "/home/meiralins/.pyenv/versions/3.5.2/lib/python3.5/signal.py", line 47, in signal
TypeError: signal handler must be signal.SIG_IGN, signal.SIG_DFL, or a callable object

I'm not sure how to fix it yet.

[justinmk]

The change seems reasonable, based on the error message in #238. I couldn't find any results on what change in asyncio made this necessary. It's somewhat surprising that it ever worked.

I'll merge this if there are no objections.

cc @bfredl @jamessan

[jamessan]

I can confirm that fixed the problem I reported.