This copies the official Docker Python images approach of stripping
the Python test suite after building from source.

For Python 3.6.2 this reduces the output from 184MB to 121MB and
removes the following directories:
```
.heroku/python/lib/python3.6/tkinter/test
.heroku/python/lib/python3.6/ctypes/test
.heroku/python/lib/python3.6/unittest/test
.heroku/python/lib/python3.6/distutils/tests
.heroku/python/lib/python3.6/sqlite3/test
.heroku/python/lib/python3.6/lib2to3/tests
.heroku/python/lib/python3.6/test
```

For Python 2.7.13 this reduces the output from 127MB to 91MB and
removes the following directories:
```
.heroku/python/lib/python2.7/ctypes/test
.heroku/python/lib/python2.7/unittest/test
.heroku/python/lib/python2.7/distutils/tests
.heroku/python/lib/python2.7/bsddb/test
.heroku/python/lib/python2.7/lib-tk/test
.heroku/python/lib/python2.7/sqlite3/test
.heroku/python/lib/python2.7/lib2to3/tests
.heroku/python/lib/python2.7/json/tests
.heroku/python/lib/python2.7/email/test
.heroku/python/lib/python2.7/test
```

Fixes #424.

commit b611ff0cd6ed05ff27a42b6c2da656441056cfba
Author: Kenneth Reitz <me@kennethreitz.org>
Date:   Fri Dec 23 23:11:51 2016 -0500

    remove debugging statements

commit d1ab8774
Author: Kenneth Reitz <me@kennethreitz.org>
Date:   Fri Dec 23 23:05:46 2016 -0500

    ln -s

commit 6844d125
Author: Kenneth Reitz <me@kennethreitz.org>
Date:   Fri Dec 23 22:55:41 2016 -0500

    further debug

commit 1346c290
Author: Kenneth Reitz <me@kennethreitz.org>
Date:   Fri Dec 23 22:54:42 2016 -0500

    debug

commit 3bc1b5e6
Author: Kenneth Reitz <me@kennethreitz.org>
Date:   Fri Dec 23 22:53:23 2016 -0500

    say when installing pip or setuptools

https://www.python.org/downloads/release/python-352/

This reverts commit ee93719b.

Conflicts:
	builds/runtimes/download_python

/cc @GrahamDumpleton