initram: start emergency shell if failed to switch to specified root

initramfs-init

@@ -125,6 +125,8 @@ if [ -n "$KOPT_root" ]; then
 	done
 	sync
 	exec /bin/busybox switch_root $NEWROOT $chart_init /sbin/init $KOPT_init_args
+	echo "initramfs emergency recovery shell launched"
+	exec /bin/busybox sh
 fi
 
 # locate boot media and mount it