always use hostname as the default broker name (pinterest#179)

In the previous implementation, we only have ` brokerStats.setName(OperatorUtil.getHostname())` when `ec2metadata` is disabled.  This is to always use hostname as broker name by default.

Author: meridional

kafkastats/src/main/java/com/pinterest/doctorkafka/stats/BrokerStatsRetriever.java

@@ -407,10 +407,10 @@ private void retrieveNetworkStats(MBeanServerConnection mbs, Set<String> topics)
    */
   private void setBrokerInstanceInfo() {
     BufferedReader input = null;
+    brokerStats.setName(OperatorUtil.getHostname());
 
     // out quick if we don't want to use ec2metadata command.
     if (disableEc2metadata) {
-      brokerStats.setName(OperatorUtil.getHostname());
       return;
     }