WIP:Use sysfs instead of the blockdev tool to determine the sector size
requested to merge frank-scheiner-guest/partman-basicfilesystems:support-grub-installs-on-newworld-powermacs into master
During Debian installation the blockdev tool always returns -1 for the sector size on NewWorld Power Macs (and maybe other machines or architectures, too), making the format operation for a FAT file system fail.
This MR makes use of sysfs instead to determine the logical sector size for the creation of FAT file systems.
Tested successfully on Mac mini G4 and Power Mac G5 (11,2).