As described, we want to set the default label for XFS disks to the
shorter value.
For example, you hit this when setting the old FS_TYPE environment
variable to 'xfs' (which sets the "root-fs-type" parameter, which gets
passed through to 'type'; but does not set a default label).
Change-Id: I41dce6e25766562db4366021309b8c2b74a8ab80
Closes-Bug: 1742170
