Query VSS backup type number (DWORD) from QEMU Guest Agent VSS Provider registry key registry value VssOption

Translate the VSS backup type number (DWORD) into its VSS backup type (VSS_BACKUP_TYPE)

Returns the queried VSS backup type if the program encounters unexpected behaviors or values return default VSS backup type VSS_BT_FULL instead

Signed-off-by: Kfir Manor <kfir@daynix.com>
Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>