To avoid repeating settings from image recipes, use a tiny Python script
to parse the original pipeline’s YAML definition and collect variables
into .env files to be sourced directly into the image building job’s
shell.

The original pipeline places the devroot tarball in a directory that
would otherwise not be accessible in this job, so we override it by
passing another -t devrootpack: argument to debos.

Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>