fixes the now-incorrect module for ApiError

https://github.com/dotcloud/docker-py/blob/0.3.2/docker/errors.py
- ApiError is now(0.3.2) under the docker.errors
support old and new versions of APIError
Merge pull request #7925 from devpopol/fixes/api_error

fixes the now-incorrect module for ApiError -- noticed since 0.3.2