Mac OS High Sierra Support

[dheaney]

Hi!

I've used image-usb-stick on previous OS X versions, and everything always worked great! I tried it High Sierra today, however, and ran into some problems. For instance, diskutil list now includes parenthetical expressions after disks:

 /dev/disk0 (internal, physical):
    #:                       TYPE NAME                    SIZE       IDENTIFIER
    0:      GUID_partition_scheme                        *121.3 GB   disk0
    1:                        EFI EFI                     209.7 MB   disk0s1
    2:                 Apple_APFS Container disk1         121.1 GB   disk0s2

It also looks like some disk attribute names have changed. This request fixes those issues.