dev_install script ready

This change makes the dev_install script functional. It will download the
necessary files to bootstrap python and emerge on a base image.

BUG=chromium-os:11502
TEST=Build base image and run dev_install in the target. Developer packages
should install correctly.

Change-Id: If9975ed8342d4924e8b0096b649847b2944a5ca0
Reviewed-on: http://gerrit.chromium.org/gerrit/5317
Tested-by: Arkaitz Ruiz Alvarez <arkaitzr@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
5 files changed