[OHAI-458] Include Joyent SmartOS specific attributes in Ohai

Hi,

This is code of OHAI-458.

Attribute Sample
----

<pre><code>
"joyent"=>
  {"sm_uuid"=>"xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
   "sm_id"=>"5",
   "sm_image_id"=>"chefserver",
   "sm_image_ver"=>"1.0.18",
   "sm_baseimage_id"=>"base64",
   "sm_baseimage_ver"=>"1.8.4",
   "sm_pkgsrc"=>"http://pkgsrc.joyent.com/sdc6/2012Q2/x86_64/All"}}</code></pre>


Test
----

<pre><code>
$ rspec -fd --color spec/unit/plugins/joyent_spec.rb 
Run options: exclude {:requires_root=>true, :ruby_18_only=>true, :windows_only=>true}

Ohai::System plugin joyent
  without joyent
    should NOT create joyent
  with joyent
    should create joyent
    under global zone
      should ditect global zone
      should NOT create sm_id
    under smartmachine
      should retrive zone uuid
      should create sm_id

Finished in 0.01397 seconds
6 examples, 0 failures

</code></pre>


Regards,