mkcephfs: magically group osds on same host into subtrees in the generated crush map
In theory we can look at the host field in the ceph.conf to generate a sane crushmap by default. As things stand, anyone running multiple cosd's on the same node has to adjust the crush map manually, which is tedious.
This could be extended (later) to do multiple levels of the hierarchy if there were other magic fields defined (in ceph.conf or elsewhere). e.g.,
host = abcdef
rack = ghi
row = jkl
Really not sure that the conf is the right place to do this, though (although it's certainly the simplest, at least right now).