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.
Could you point me where the doc describe this? Or it is Tizen only? 

And agree with @rakuco, with historic reason, we use different api to get the storage info for desktop and Tizen.  If you  unify to use udev, that would be great.