Add modules for Hardware Testing

dosfstools: used when creating the grub-based boot image
parted: used when installing and when creating boot iamges

https://bugzilla.gnome.org/show_bug.cgi?id=732394
Switch to an external kernel build

Don't include the kernel or kernel-derived headers in gnomeos trees;
include bc in the devel tree since recent kernels depend on it for
building. (Earlier kernels used perl for arbitrary precision
calculations.)

https://bugzilla.gnome.org/show_bug.cgi?id=732395