feed osd info about os, kernel, memory, arch to the mons

<pre>
$ ceph osd metadata 0
{ "arch": "x86_64",
  "ceph_version": "ceph version 0.72-225-g5f35915 (5f359155c54c936f83db530015f9e1c3b4e603ad)",
  "distro": "Ubuntu",
  "distro_codename": "raring",
  "distro_description": "Ubuntu 13.04",
  "distro_version": "13.04",
  "hostname": "nine",
  "kernel_description": "#44-Ubuntu SMP Thu Aug 22 20:52:24 UTC 2013",
  "kernel_version": "3.8.0-30-generic",
  "mem_swap_kb": "3888124",
  "mem_total_kb": "3614540",
  "os": "Linux"}
</pre>