[UI, API] more control over parition naming / ordering

When creating partitions on a 'named' disk, there is little influence on the naming of the partition.
They get named like: <disk name>-part#.

The problem is that if an mistake has been made, e.g. a partition is added and later removed. This is not resembled in the name that is assigned to the partition. So one can end up with a disk e.g. md0 have a partition labeled like; md0-part10, as it took multiple iterations to get the partition right.

This is a problem for a roll-out, as some tools depend on consistent naming, which is not possible to get done this way.
Redoing the commissioning is not always an option, as that means that all disks have to be redone, even the ones that are fine. Which is quite time-consuming.