PRODUCT_OTA_PUBLIC_KEYS is meant to be set by a vendor tree, something
we don't use.
Override it at the source and set it explicitely as well.
This ensures that the compiled recovery.img and the one generated by
sign_target_files_apks.py includes the real public keys for verification.
11.0 signing is ignored.
This will need to be extensively tested as breakage can mean brick on locked
devices.
Although in failure cases it seems test-keys are accepted.
--
After much testing there appears to be a deeper issue with how keys
are inserted into the recovery and handled
- Disable generation of unused OTA to reduce compile time
- 17.1+: Disable APEX, breaks signing, and is also useless since no Play Store.
- 18.1: Fixup signing
