run_qemu.sh: use an exit trap for reporting the result and cleanup

This will prevent any leftover files in case of a sudden error or
ctrl+c.

run_qemu.sh

@@ -5,6 +5,24 @@ set -eu
 cachedir="./shared/cache"
 tmpdir="$(mktemp -d)"
 
+cleanup() {
+	rv=$?
+	rm -f "$tmpdir/debian-unstable-overlay.qcow"
+	[ -e "$tmpdir" ] && rmdir "$tmpdir"
+	if [ -e shared/result.txt ]; then
+		head --lines=-1 shared/result.txt
+		res="$(tail --lines=1 shared/result.txt)"
+		rm shared/result.txt
+		if [ "$res" -ne 0 ]; then
+			# this might possibly overwrite another non-zero rv
+			rv=1
+		fi
+	fi
+	exit $rv
+}
+
+trap cleanup INT TERM EXIT
+
 # the path to debian-unstable.qcow must be absolute or otherwise qemu will
 # look for the path relative to debian-unstable-overlay.qcow
 qemu-img create -f qcow2 -b "$(realpath $cachedir)/debian-unstable.qcow" "$tmpdir/debian-unstable-overlay.qcow"
@@ -18,10 +36,3 @@ qemu-system-x86_64 $KVM -m 512M -nographic \
 	-serial unix:/tmp/ttyS1,server,nowait \
 	-virtfs local,id=mmdebstrap,path="$(pwd)/shared",security_model=none,mount_tag=mmdebstrap \
 	-drive file="$tmpdir/debian-unstable-overlay.qcow",cache=unsafe,index=0
-head --lines=-1 shared/result.txt
-if [ "$(tail --lines=1 shared/result.txt)" -ne 0 ]; then
-	echo "test.sh failed"
-	exit 1
-fi
-rm "$tmpdir/debian-unstable-overlay.qcow" shared/result.txt
-rmdir "$tmpdir"