build_image: move python/portage symlinks to the base image

This fixes running emerge and such after `dev_install` on a base image.
This used to work when we only needed /usr/bin/python, but this broke a
while back.  We fixed it for dev images, but base images stayed broken.

BUG=chromium:701955
TEST=precq passes
CQ-DEPEND=CL:1512811

Change-Id: I039aa8b11e735214ecfc3bbe458e51f59be5be89
Reviewed-on: https://chromium-review.googlesource.com/1514092
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
2 files changed