UMS support with any volume, not only primary (2/3)

This patch enables UMS support when any volume supports it, even when the
primary storage doesn't.
1. Vold: assign lun_numbers sequentially to the volumes being added to the
   VolumeManager.
2. Fix portions of code which assume that the device has UMS support iff the
   primary storage supports UMS.
   Instead, determine whether the device supports UMS by checking each volume.
3. Display the UMS option in Settings.apk when any volume supports it.