Sanitize create_container input

Client.create_container takes a volumes_from argument that should be: a
string, a list of strings, or None. If an empty list or dict is passed
instead, the docker daemon returns a 406 Client Error: Not Acceptable
Add test to check for the absence of volumes_from
Missed empty line for flake8
Relative 'errors' imports, for consistency
Merge pull request #198 from fcoelho/fix-volumes-from

Sanitize create_container input for volumes_from
Merge pull request #211 from aanand/relative-errors-imports

Relative 'errors' imports, for consistency
Universally-compatible reading of chunked streams

Docker introduced newlines in stream output in version 0.9
(https://github.com/dotcloud/docker/pull/4276), but not to all
endpoints - POST /images/create, for example, does not include them.

This reverts to the old, less pleasant implementation of
_stream_helper(), with a manual check for newlines to fix the problem
described in #176 and fixed in #184, without the accompanying
regression. It should work against Docker 0.8, 0.9 and 0.10, both when
building and when pulling.