Combine ISO generation steps
This folds adding hydra-build-products into the actual ISO generation,
preventing an unnecessary download of the ISO.
(cherry picked from commit 10293b87a9da30631b49b11b56cd8a55dd3c7896)
Signed-off-by: Domen Kožar <domen@dev.si>
authored by Eelco Dolstra and committed by Domen Kožar d24e4eef fa4b5605