Enable multiple overlayfs architecture (to include persistant structure)

[Jacob Galbreath]

Currently squashfs/overlayfs architecture only support a single overlayfs on top of a read-only squashfs image.

Preferably Neuvoo should allow injection of multiple overlays be set up prior to loading the entire system.

Example overlay1 "OS software patch 1" overlay2 "OS software patch 2" overlay3 "Neuvoo Service Pack?" overlay4 "persistant config files"

References https://docs.docker.com/engine/userguide/storagedriver/overlayfs-driver/ https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt