Align the partition end sectors and add partition names

sgdisk by default only aligns the partition start. Use the --align-end option to align the partition end too.

Additionally:

* Add PARTLABEL values to all partitions.
* Do not hardcode the partition number and end sectors in sgdisk commands by using the special value "0".
* Follow the Discoverable Partitions Specification by using the "Linux x86-64 root" partition type.
6 jobs for sgdisk-align-end in 11 minutes and 24 seconds (queued for 1 second)