Fixups to hold excelsior on chef

- Add android-core package to packages.mk. This is in build/ on
master/day, but not chef.
- Add coral-edgetpu-stable to multistrap list, to get python3-edgetpu

Change-Id: I20b66b9cec9617aaee73fcf6b8142a40f80726c5
(cherry picked from commit b3c50256e62368523d6d3453f1a5e7e22a5c394b)