The --extract_update option used to do exactly that, just extract the
USR-A partition for updates and no more. Now it does the same thing as
--generate_update, except it names the file flatcar_test_update.gz
rather than flatcar_production_update.gz. --generate_update is never
actually used because official update payloads are manually generated
with the generate_payload script later on.
Resolve this confusion by deduplicating the common code between them.
Any update payload produced during this stage of the build is only
useful for testing, so change --generate_update to always create
flatcar_test_update.gz. --generate_update now implies --extract_update
and both are enabled by default.
Signed-off-by: James Le Cuirot <jlecuirot@microsoft.com>
e44b946abf