Fix volumes to publish the real confluence_home path

This was one of the steps I needed to take to get persistent data stored outside of the container.  If nothing else, this change allows the confluence_home directory to be viewed from a child container that links to this one.

The other change I needed to make locally was removing the `USER nobody:nogroup` directive, as this was causing permission errors when the volume is mounted from a linked container.  Not sure how you'd feel about removing that and running the service as root.