Ganglia input: Store the value and ganglia name.

Previously, we only had metadata in events, which wasn't very useful. An event would look like
this:

    {
          "@version" => "1",
        "@timestamp" => "2014-09-22T10:51:59.337Z",
          "log_host" => "example.com",
              "dmax" => 0,
              "tmax" => 90,
             "slope" => "both",
              "type" => "float",
             "units" => "%",
              "host" => "1.2.3.4"
    }

Events now look like this:

    {
          "@version" => "1",
        "@timestamp" => "2014-09-22T10:51:59.337Z",
          "log_host" => "example.com",
               "val" => 0.0, # added
              "dmax" => 0,
              "tmax" => 90,
             "slope" => "both",
              "type" => "float",
             "units" => "%",
              "name" => "cpu_nice", # added
              "host" => "1.2.3.4"
    }