updated xml for tb 3.0.0

I just pulled this XML from the 3.0.0 package and replaced the ModCluster and Peers variables.

You can use this by overriding ```z:ha_server_config_template``` in your role to ```standalone-ha-3.0.x-incremental.xml.erb```:

    default_attributes({
      :torquebox => {
        :ha_server_config_template => "tb3-standalone-ha.xml.erb",
      }
    })