Generate demo mode resources during image build

Updates build_image to create imageloader supported image from test demo
mode resourced directory created under local rootfs build directory
(which are finalized during base image finalization), and install them
to the test image.
Also, generates standalone demo mode resources artifact (that is
intended to eventually be added to appropriate images' stateful
partitions during factory flow).

BUG=chromium:827363
TEST=build image

Change-Id: Ie05e71e966b755926a80a2405d3a3ca736a024de
Reviewed-on: https://chromium-review.googlesource.com/1069997
Commit-Ready: Toni Barzic <tbarzic@chromium.org>
Tested-by: Toni Barzic <tbarzic@chromium.org>
Reviewed-by: Wei-Han Chen <stimim@chromium.org>
4 files changed