Add support for privileged containers. Refs #123

This is required for mounting external volumes and
addresses errors such as `mount.nfs: Operation not permitted`

Be gentle, I don't use Python normally :)

Revert changes to docker package client.py

Priviliged is only required for starting containers, not for creating them

Only make container priviliged when True is specified

Only delete priviliged for create when it's set (Should fix travis fails)