Replace old index image with hub

Docker-DCO-1.1-Signed-off-by: Brian Goff <cpuguy83@gmail.com> (github: cpuguy83)
Fix more instances of "dotcloud/docker" in hack/ (and add a DOCKER_PKG environment variable to simplify references to our "package path" in our bundlescripts)

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Check for OS and root privileges in NewDaemon

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Move TMPDIR symlink cleanup to NewDaemon

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Move canonical root path detection to NewDaemon

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Move kernel version/capabilities detection to NewDaemon

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)