Implement the detection of USB Flash devices on IVI.

BUG=XWALK-2040

This patch implement the feature of detecting USB Flash devices on ivi, as well as getting its "capacity" and "isRemovable" attributes.
https://developer.tizen.org/dev-guide/2.2.0/org.tizen.web.device.apireference/tizen/systeminfo.html#::SystemInfo::SystemInfoStorageUnit