luv-live-image: Pick fat32 fstype when creating partitions

If no file system type is specified when creating partitions using
parted (as is currently the case in the luv-live-image recipe) a default
value is used, which happens to be 83 (Linux).

Brian reports that this is causing the luv-results partition to not be
mounted and displayed correctly on his Windows 7 machine, and that some
of the Windows disk management tools are getting kinda confused.

Specify "fat32" when creating partitions, so that the partition label
matches reality.

Reported-by: Brian Richardson <brian.richardson@intel.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>