curtin ignores uuid on a partition

[Michael Hudson-Doyle]

Curtin's block device schema and some examples (but not the documentation) put a 'uuid' on 'type': 'partition' actions. But nothing reads this value and does anything with it -- partitions end up with autogenerated UUIDs (I'm also not sure what setting this value _should_ do with an msdos partition table -- but for a gpt it's clear).

[Michael Hudson-Doyle (mwhudson)]

Oh I see the schema says:

        'uuid': {'$ref': '#/definitions/uuid'}, # XXX: This is not used

but even so...

[Ryan Harper (raharper)]

It's unfortunate that sgdisk doesn't take the uuid in the --new parameter list. So this involves as second exec of sgdisk with --partition-guid=<number>:guid