ceph-disk: rework get_partition_{type,uuid}

ceph-disk: rework get_partition_{type,uuid}

Mimic the get_partition_type implementation after get_partition_uuid
and factorize them to reduce the code footprint.

The get_partition_type implementation is based on blkid: it is complex
and fragile. Since sgdisk is consistently used to create partitions, use
it instead. It is already used for get_partition_uuid and there does not
seem to be any reason for concern.

http://tracker.ceph.com/issues/11881 Refs: #11881

Signed-off-by: Loic Dachary <ldachary@redhat.com>