Bind-mount container's config.json for introspection

Use this for introspection.

Closes #1270 #7255

I looked at doing things like mounting a socket into each container for introspection, and even have a project @ github.com/cpuguy83/lestrade that does just this.
But this would require lots and lots of design discussion, and a lot of complexity, when really all that's needed is the json data, which is already there in the container's root config path, so let's just bind-mount that in.

Docker-DCO-1.1-Signed-off-by: Brian Goff <cpuguy83@gmail.com> (github: cpuguy83)