build_packages.sh: Move completion msg to Python

Migrate the command completion message (including info about how long
the command took to run) to Python.

BUG=b:218522022
TEST=CQ

Cq-Depend: chromium:3661367
Change-Id: I7973e368619d043a5ceafdbe2010842a377c15d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3661663
Commit-Queue: Cindy Lin <xcl@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Cindy Lin <xcl@google.com>
1 file changed