update hooks: slip in public rambi overlay

For people who have rambi builds already, regen their board configs
so that they also include the public overlay.

CQ-DEPEND=CL:174384

BUG=None
TEST=`./update_chroot` converts a private-only /build/rambi to include
the public repo

Change-Id: I948de94d4e00afc008c8544c9edf7d443533578c
Reviewed-on: https://chromium-review.googlesource.com/174440
Reviewed-by: Bernie Thompson <bhthompson@chromium.org>
Commit-Queue: Bernie Thompson <bhthompson@chromium.org>
Tested-by: Bernie Thompson <bhthompson@chromium.org>
1 file changed