feat(build_library): generate squashfs in cpio

squashfs is more efficient and plays well with namespaces. Switch to
generating a cpio with a single squashfs files.
feat(vm_image_util): use bind mounts for pxe oem

solid cleanup idea from marineam to use bind mounts instead of copying
to generate the desired root layout.
fix(vm_image_util): remove /usr/share/oem prefix

remove this prefix from the PARTIIONED=0 builds
Merge pull request #113 from philips/squashfs-init

feat(build_library): generate squashfs in cpio