Switch base image to debian

This also updates the apt-get commands to be inline and reduce the
number of layers.  It adds cpio because debian does not include
the app by default.
Move make_iso.sh into Dockerfile

We can move this into the dockerfile now because build supports MKNOD.
I also updated the build docs to suggest using cat to get the iso out of
the image.
Merge pull request #325 from crosbymichael/update-dockerfile

Switch to debian as the base image and move make_iso into dockerfile