Run eclean by default to clear out binary packages in case of a revert.

This adds eclean early in make_chroot, update_chroot, and
build_packages to clear out binary packages that correspond to ebuilds
that have been removed or reverted.

BUG=chromium:1202194
TEST=CQ passes

Change-Id: Ie519aa547bb63743375d4fd9b83d1b11f0ef11ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2848595
Tested-by: Allen Webb <allenwebb@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Allen Webb <allenwebb@google.com>
3 files changed