Use actual storage type of sdcard/usb (2/2).

Currently, storage volume description for mount/unmount/format determined at
build time using PRODUCT_CHARACTERISTICS. For device which has only a sdcard or
only support usb storage, displayed description is correct. For device which has
both storage, the displayed description is totally wrong.

Use of actual storage type at runtime can eliminate the needed to specify
product characteristics, either default or nosdcard.

Change-Id: I9f8d53a4648d960f1009b1fe94787eecd4343427