ceph: osd_belongs_to_node: only check tree-entries of type host, refactor

ceph: osd_belongs_to_node: only check tree-entries of type host, refactor

We want to check explicitly for type host, so filter for that first
and create a hash map for easier usage afterwards.

Drop the error when there's no tree, as either RADOS error'd on bad
command already, or there really is no tree (but RADOS worked OK), in
which case we simply return that the OSD did not belong to this node.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>