Using a log2n way to fill a much smaller buffer, and receiving in a cleaner way with EOF.
The failing test was reproducible using the following command thanks to @aeros :
```bash
./python -m test test_asyncio.test_sock_lowlevel --match test_sock_client_racing -j100 -F -v
```
According to test results, we may still need to bump the timeout:
5aad027db9/Lib/test/test_asyncio/test_sock_lowlevel.py (L256-L257)
Skip new "racing" socket tests which fail randomly until someone fix
them, to ease analysis of buildbot failures (skip tests which are
known to be broken/unstable).
* Move socket related functions from test.support to socket_helper.
* Import socket, nntplib and urllib.error lazily in transient_internet().
* Remove importing multiprocess.
Victor Stinner
Alex Grönholm
Andrew Svetlov
Nikita Sobolev
Serhiy Storchaka
Fantix King