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
Hack to fix #7738: Allow tag in image parameter of docker module

It also defaults to the "latest" tag for pulling the image
instead of pulling all versions.
Merge remote-tracking branch 'kolloch/devel' into docker_fixes
Merge remote-tracking branch 'discordianfish/docker-add-net-parameter' into docker_fixes