build_packages: allow people to specify a specific set of packages

This way we can tweak buildbot configs to install specific packages rather
than all of ChromeOS (useful for firmware builders).

BUG=chromium-os:19140
TEST=`cbuildbot {{x86,amd64}-generic,daisy}-paladin {amd64,arm,x86}-generic-full stout-release` passed
TEST=`./build_packages nano` installed just nano

Change-Id: I9c316d7c390ebe6ceade97cf33c1387dc83fb887
Reviewed-on: https://gerrit.chromium.org/gerrit/33266
Reviewed-by: Brian Harring <ferringb@chromium.org>
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/35318
1 file changed