Allows creating multiple OSDs on a single (NVMe) block device,
leveraging the "ceph-volume lvm batch" command. Replaces the previous
method of creating OSDs.
Also adds a new ZK item for each OSD indicating if it is split or not.
Adds a new API query parameter to define the file size, which is then
used for the temporary image. This is required for, at least VMDK, files
to work properly in qemu-img convert.
