PRQ-136: Fix the ganglia input so it works with Hadoop.  Add unit test.

Running:
{code}
lfo$ ruby -rgmetric -e 'Ganglia::GMetric.send("127.0.0.1", 8649, { :name => "pageviews", :units => "req/min", :type => "uint16", :value => 7000, :tmax => 60, :dmax => 300, :group => "test" })'
{code}

Now yields:
{code}
lfo$ bin/logstash agent -e 'input { ganglia { type => "nerve" } }'
Using milestone 1 input plugin 'ganglia'. This plugin should work, but would benefit from use by folks like you. Please let us know if you find bugs or have suggestions on how to improve this plugin.  For more information on plugin milestones, see http://logstash.net/docs/1.4.0.rc1/plugin-milestones {:level=>:warn}
{
      "@version" => "1",
    "@timestamp" => "2014-03-14T21:47:31.350Z",
      "log_host" => "",
          "name" => "pageviews",
           "val" => "7000",
          "dmax" => 300,
          "tmax" => 60,
         "slope" => "both",
         "units" => "req/min",
         "vtype" => "uint16",
          "type" => "nerve",
          "host" => "127.0.0.1"
}
^C
{code}

Note the "val" field has a 7000 and that "uint16" is the value of "vtype" and "type" is "nerve".