Update parallel_emerge to use Portage APIs to grab package information.

This results in a more accurate package DB. It also fixes the issue
where parallel_emerge sleeps when it can't get the package URL.

BUG=chromium-os:12312
TEST=Try merging some packages

Change-Id: I48315497b9dae552be5785d083f5c5a93a500379

R=nsanders@chromium.org

Review URL: http://codereview.chromium.org/6728018
1 file changed