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.
I'd prefer
```
switch (type) {
  case INTERNAL:
    return "INTERNAL";
  case USB_HOST:
    return "USB_HOST";
  case MMC:
    return "MMC";
  case UNKNOWN:
  default:
    return "UNKNOWN";    
}
```