fix(build_image): Remove defunct bootcache option.

From ChromeOS, not applicable to our systems.
cleanup(*): Remove unused/broken test and factory images
cleanup(path-overrides): Remove unused directory
fix(build_image): Install dev packages into root, not /usr/local.

We don't have any particular reason for the weird hackery required to
install packages into /usr/local instead of root. The rootfs image is
already being modified a little might as well modify it a lot. :)
fix(build_image): Replace two lingering pbzip2 references with lbzip2
fix(build_image): Exclude libc locales and info pages.
fix(build_image): Always use read-write for developer images.
Merge pull request #114 from marineam/image-cleanup

Image cleanup