STORM-200 Proposal for Multilang's Metrics feature

for https://issues.apache.org/jira/browse/STORM-200

Storm 0.9.0.1 exposes a metrics interface to report summary statistics across the full topology. We can build our own metric, and build metrics consumer to use those statistics. 

But when we use Multilang(ie. Python), we can not use this feature. So we want to summit a proposal for multilang's metrics. 

The specifics of the proposal: 
1. The main idea is: when user want to add a metric statistics in multilang(python) bolt， 
    a) he need first create a metric object and register in ShellBolt's sub-class, 
    b) then update the metric in Python bolt process through RPC call. 

2. In Metrics API: 
    a) extend IMetric interface add a method for RPC call：
                   public void updateMetricFromRPC(List<Object> params); 
    b) modify IMetric implements, to support updateMetricFromRPC; 

3. In ShellBolt， 
    a) we have a Map<String, IMetric> to hold user's registered metrics object； 
    b) we have a method registerMetric(String name, T metric) for user to register their metrics object; 
    c) we have a method handleMetrics(Map action) to handle RPC call from Python process； 

4) In Multilang protocol: add a command "metrics" for shell process to make RPC call. The protocol is: {"command":"metrics", "name":"metric-registerd-name", "params":["param-1", param-2]} 

5) In storm.py：add rpcMetrics(name, params), user can update remote metric through this RPC call. 

--------ExamplePythonBolt.java----------------------------------------------------------------------------------------------------
public class ExamplePythonBolt extends ShellBolt implements IRichBolt {
	private static final long serialVersionUID = 1999209252187463355L;

	private TopologyConfig topologyConfig;
	
	public ExamplePythonBolt(TopologyConfig config) {
		super("python", "ExampleBolt.py", config.topologyName);
		topologyConfig = config;
	}
	
    public void prepare(Map stormConf, TopologyContext context, OutputCollector collector) {
    	super.prepare(stormConf, context, collector);
    	
    	CountMetric cMetric = new CountMetric();                         //generate a metric object
    	context.registerMetric("PythonBoltCount", cMetric, 120);  //register metric object to context
    	this.registerMetric("PythonBoltCount", cMetric);                //register metric object to ShellBolt
    }

	public void declareOutputFields(OutputFieldsDeclarer declarer) {
		declarer.declare(new Fields("LogRecord"));
	}

	public Map<String, Object> getComponentConfiguration() {
		return null;
	}
}

--------ExampleBolt.py---------------------------------------------------------------------------------------------------
class ExampleBolt(storm.BasicBolt):
    def __init__(self, boltParams):
        #from here, you can get params from java
        pass
    
    def initialize(self, stormconf, context):
        pass
        
    def process(self, tup):
        try:         
            
            MTLOGGER.info("TestAction", "handle the json %s" % (logjson))  
            storm.emit([tup[0]])
            
            storm.rpcMetrics("PythonBoltCount", [1])        //update your PythonBoltCount metric with param list "[1]"
        except Exception,tx:
            //handle error