Backend: underps and regression fixes

- fallback by-name system mount may still result in /system at /system_root so add back check
- add missing /persist mountpoint

META-INF/com/google/android/update-binary

@@ -144,19 +144,20 @@ mount_all() {
       fi;
     ;;
   esac;
+  [ -f /system_root/system/build.prop ] && system=/system;
   for mount in /vendor /product /system_ext; do
-    if ! is_mounted $mount && [ -L /system$mount -o -L /system_root$mount ]; then
+    if ! is_mounted $mount && [ -L /system$mount -o -L /system_root$system$mount ]; then
       setup_mountpoint $mount;
       $BB mount -o ro -t auto /dev/block/$byname$mount$slot $mount;
     fi;
   done;
   if is_mounted /system_root; then
     mount_apex;
-    $BB mount -o bind /system_root /system;
+    $BB mount -o bind /system_root$system /system;
   fi;
   if ! is_mounted /persist && [ -e /dev/block/bootdevice/by-name/persist ]; then
     setup_mountpoint /persist;
-    $BB mount -o ro -t auto /dev/block/bootdevice/by-name/persist;
+    $BB mount -o ro -t auto /dev/block/bootdevice/by-name/persist /persist;
   fi;
 }
 umount_all() {