add an option to not self-update the script.

general/overlay/usr/sbin/sysupgrade

@@ -200,6 +200,7 @@ Where:
       --force_all      do not validate anything
   -n, --wipe_overlay   wipe overlay partition
   -x, --no_reboot      do not reboot after updating
+  -z, --no_update      do not update self
   -h, --help           display this help and exit
 "
 }
@@ -276,6 +277,10 @@ for i in "$@"; do
 			skip_reboot=1
 			shift
 			;;
+		-z | --no_update)
+			skip_selfupdate=1
+			shift
+			;;
 		*)
 			print_sysinfo
 			echo_c 37 "\nUnknown option: $1"
@@ -293,7 +298,7 @@ print_sysinfo
 	echo_c 37 "\nTry '$(basename "$0") --help' for options." &&
 	exit 0
 
-self_update
+[ "1" != "$skip_selfupdate" ] && self_update
 
 check_sdcard