Let udev settle between writing partition flags and formatting. (#1109244)
Remove unused fallback code from DiskLabel.

This is not used, and the partitions part would cause calling code
to fail anyway since it all expects a list of parted.Partition instances.
Change signature of DiskLabel.addPartition to be more useful.

The new method accepts start sector, end sector, and partition type.

The previous method required you to pass in a parted.Partition instance.
It did not simply add that parted.Partition instance. Instead, it created
a new parted.Partition instance based on the one passed in and added that
to the parted.Disk.