Add devel/py-subprocess32, Backport of the subprocess module from Python 3.2 & 3.3

This is a backport of the subprocess standard library module
from Python 3.2 & 3.3 for use on Python 2. It includes bugfixes
and some new features. On POSIX systems it is guaranteed to
be reliable when used in threaded applications. It includes
timeout support from Python 3.3 but otherwise matches 3.2's API.
It has not been tested on Windows.

WWW: https://github.com/google/python-subprocess32

PR: 222628
Submitted by: Sebastian Schwarz <seschwar@gmail.com>
Reviewed by: koobs, sunpoet
Differential Revision: D12519