When creating a zpool and formatting tons of disks we're running kern.geom.confxml for EACH disk which is brutally painful. The method responsible for doing this is running this just to get the size and the sectorsize of the disk. There is 0 reason to parse the entirety of geom xml information just to parse these 2 values. There is already a `get_size_with_name` method in py-bsd which uses ioctl to query the disk directly. A new method `get_sectorsize_with_name` needs to be added to py-bsd so we can get this information without parsing all of xml.