feature request: deploy OSDs with mixed disk layouts

[m-ildefons]

Currently, nodes with the storage role have a given number of disk drives, all with the same given size, but sometimes it is required that nodes are provisioned with a mix of drives with different characteristics, size being the easiest one to modify.
These extravagant disk layouts could be created by specifying --num-disks and --disk-size multiple times, e.g.

$ sesdev create ses7p --num-disks 2 --disk-size 10 --num-disks 2 --disk-size 20

resulting in a ses7p cluster where each node with the storage role has two drives of 10GiB size and two drives of 20 GiB size in addition to the root drive.
When --disk-size is not specified often enough, the remaining drives will be created with default size, if it is specified more often than --num-disks, the superfluous arguments will be ignored.
This feature would be a great help when testing OSD deployment processes and drive group configuration.