Configuring chef-client to load custom ohai-plugins:

1. edit /etc/chef/client.rb
2. add the following line to the end of the file:

   Ohai::Config[:plugin_path] << '/etc/ohai/plugins' #you can choose any path you want

3. add your custom plugins there (i.e. /etc/ohai/plugins)
4. reload the client:
   /etc/init.d/chef-client restart