Expand trap cleanup function (#773)

* 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

---------

Co-authored-by: Serge Schneider <serge@raspberrypi.com>

scripts/common

@@ -58,9 +58,12 @@ unmount(){
 export -f unmount
 
 unmount_image(){
-	sync
-	sleep 1
-	LOOP_DEVICE=$(losetup --list | grep "$1" | cut -f1 -d' ')
+	if command -v udevadm >/dev/null 2>&1; then
+		udevadm settle 10
+	else
+		sleep 1
+	fi
+	LOOP_DEVICE=$(losetup -n -O NAME -j "$1")
 	if [ -n "$LOOP_DEVICE" ]; then
 		for part in "$LOOP_DEVICE"p*; do
 			if DIR=$(findmnt -n -o target -S "$part"); then