partially fix #2285: ui: ceph: allow selecting partitions

partially fix #2285: ui: ceph: allow selecting partitions

For DB and WAL disks, not only partitions will show up now, but one
more type of disk, that didn't show up before: Namely, GPT-partitioned
disks with any partitions detected as used.

It's confusing as the size shown is of the full disk, with no
indication that a new partition will be appended at the end. This
problem was already present before, but only affected GPT-partitioned
disks where no usage on a partition was detected.

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>