image_signing: tweak loem firmware signing to have real keys

Rather than leave the default set of keys in the firmware untouched
(which are dev keys), insert the first loem keyset we find.  This is
for people who extract the bios.bin by hand and then blindly burn it
into their flash.  This way they'll still get some valid loem keys.
It's not a great solution, but it's better than nothing.

BUG=chromium:381862
TEST=signed recovery image by hand w/loemkeys and looked at packed bios.bin
TEST=signed recovery image by hand w/devkeys and looked at packed bios.bin
TEST=signed recovery image by hand w/custom loemkeys and looked at packed bios.bin
BRANCH=none

Change-Id: I8db1e34d9f4d85be6edf81fecf79a72031571b01
Reviewed-on: https://chromium-review.googlesource.com/204262
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
2 files changed