build/tools: Fix image downloading issue for esp32 board.
build/tools: Fix image downloading issue for esp32 board.

	Modify the image downloading command from "make download APP" to "make download OS".

an4967/TizenRT,chanijjani/TizenRT,an4967/TizenRT,junmin-kim/TizenRT,chanijjani/TizenRT,jeongchanKim/TizenRT,pillip8282/TizenRT,chanijjani/TizenRT,davidfather/TizenRT,junmin-kim/TizenRT,sunghan-chang/TizenRT,sunghan-chang/TizenRT,jeongarmy/TizenRT,chanijjani/TizenRT,jeongarmy/TizenRT,jsdosa/TizenRT,Samsung/TizenRT,sunghan-chang/TizenRT,pillip8282/TizenRT,an4967/TizenRT,an4967/TizenRT,jsdosa/TizenRT,jeongchanKim/TizenRT,chanijjani/TizenRT,an4967/TizenRT,sunghan-chang/TizenRT,Samsung/TizenRT,jeongchanKim/TizenRT,pillip8282/TizenRT,jeongchanKim/TizenRT,an4967/TizenRT,jeongchanKim/TizenRT,chanijjani/TizenRT,jeongchanKim/TizenRT,jsdosa/TizenRT,Samsung/TizenRT,jeongarmy/TizenRT,jeongarmy/TizenRT,pillip8282/TizenRT,junmin-kim/TizenRT,chanijjani/TizenRT,junmin-kim/TizenRT,jsdosa/TizenRT,jsdosa/TizenRT,sunghan-chang/TizenRT,sunghan-chang/TizenRT,Samsung/TizenRT,jsdosa/TizenRT,pillip8282/TizenRT,davidfather/TizenRT,sunghan-chang/TizenRT,jsdosa/TizenRT,jeongarmy/TizenRT,jeongarmy/TizenRT,jeongchanKim/TizenRT,jeongarmy/TizenRT,Samsung/TizenRT,pillip8282/TizenRT,junmin-kim/TizenRT,davidfather/TizenRT,junmin-kim/TizenRT,davidfather/TizenRT,davidfather/TizenRT,Samsung/TizenRT,an4967/TizenRT,Samsung/TizenRT,pillip8282/TizenRT,junmin-kim/TizenRT,davidfather/TizenRT,davidfather/TizenRT