Set CROS_ARTIFACTS_TMP_DIR for ebuilds.

For a given package, CROS_ARTIFACTS_TMP_DIR is set to a directory
where ebuild artifacts can be stored. During merging, these
are moved to "/var/lib/chromeos/package-artifacts/${CATEGORY}/${PF}"
if merging succeeds, or to
"/var/lib/chromeos/package-artifacts/${CATEGORY}/${PF}-failed"
otherwise.

BUG=b:187795688
TEST=CQ

Change-Id: I74eeb68695d9bfb492a53589ca2d5a38dae4f99c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/portage_tool/+/3625991
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Michael Benfield <mbenfield@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
2 files changed