* build.sh: Unmount intermediates on trap
Iterate through image files which might be in use and detach them
Avoid silent failures - let the user know whether the build failed
* common: update unmount_image
Use udevadm settle instead of sleep if possible
Use losetup's -j option to find the loop device associated with a give image file
* build.sh: update clean-up trap term
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Co-authored-by: Serge Schneider <serge@raspberrypi.com>
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