Add busybox rootfs so we can run containers

make sh will spawn a new container using the minimal.json file inside
busybox and you don't even know what is going on.
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
Merge pull request #120 from crosbymichael/add-tests1

Add busybox rootfs so we can run containers
Add missing "--rm" on "make sh"

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #122 from tianon/makefile-rm

Add missing "--rm" on "make sh"
netlink_linux: add remove address call, refactor add address call to
share code with remove address call.

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
netlink/netlink_linux_test.go: tests for netlink add/rem ip

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)