Disks: return correct journal disk candidates

Disks: return correct journal disk candidates

Previously any GPT initialized disk without an osdid (i.e. equal to -1) would
be included in the list of journal disk candidates, for example a ZFS disk. But
the OSD creation API call will fail for those. To fix it, re-use the condition
from the corresponding check in that API call (in PVE/API2/Ceph/OSD.pm).
Now, included disks are unused disks, those with usage 'partitions' and GPT, and
those with usage 'LVM'.

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