Add networking mode parameter (net) to docker

Since 0.11 Docker supports different networking modes (see docker run
--net). This commit add support for that to the ansible docker module.

This depends on
https://github.com/dotcloud/docker-py/commit/2d58351164eba01e30569f44a921d5aca40163ae
Merge branch 'docker-add-net-parameter' of https://github.com/discordianfish/ansible into discordianfish-docker-add-net-parameter
Updating version_added for docker net param and adding an example
Merge branch 'discordianfish-docker-add-net-parameter' into devel