implement osd list

Perform a bunch of things to be able to get the metadata needed for osd list.

It looks into `ceph osd tree` in a monitor node and tries to find OSD info there, and if available it will use it, on top of reading some files in the common OSD paths.

Finally it also calls ceph-disk to try and see where the OSD is actually mounted.

 
![04-23-2014-15-48-17](https://cloud.githubusercontent.com/assets/317847/2782838/d4c6a098-cb25-11e3-9621-df70c4712a32.png)