sample.ceph.conf: minor update

 * Moved filestore settings above [osd.*] declarations otherwise
   (if uncommented) those settings might be applied only to last
   OSD which is not very obvious.
 * Few options added.
Merge pull request #1816 from onlyjob/docs

sample.ceph.conf: minor update

Reviewed-by: Greg Farnum <greg@inktank.com>