When partition scheme is GPT*, bsdinstall still use partition name instead of gpt label for swap partition when updating fstab.
this patch will use gpt label instead partition name.
A useful scenario is, after the system is installed, if users add more disks or change the disk sequence, this behavior will make zroot disk name change. if fstab uses the fixed partition name, the user should update fstab too. while using the gpt label. it is always correct.