[SPARK-5401] set executor ID before creating MetricsSystem

Author: Ryan Williams <ryan.blake.williams@gmail.com>

Closes #4194 from ryan-williams/metrics and squashes the following commits:

7c5a33f [Ryan Williams] set executor ID before creating MetricsSystem

core/src/main/scala/org/apache/spark/SparkEnv.scala

@@ -326,6 +326,10 @@ object SparkEnv extends Logging {
       // Then we can start the metrics system.
       MetricsSystem.createMetricsSystem("driver", conf, securityManager)
     } else {
+      // We need to set the executor ID before the MetricsSystem is created because sources and
+      // sinks specified in the metrics configuration file will want to incorporate this executor's
+      // ID into the metrics they report.
+      conf.set("spark.executor.id", executorId)
       val ms = MetricsSystem.createMetricsSystem("executor", conf, securityManager)
       ms.start()
       ms

core/src/main/scala/org/apache/spark/metrics/MetricsSystem.scala

@@ -130,8 +130,8 @@ private[spark] class MetricsSystem private (
       if (appId.isDefined && executorId.isDefined) {
         MetricRegistry.name(appId.get, executorId.get, source.sourceName)
       } else {
-        // Only Driver and Executor are set spark.app.id and spark.executor.id.
-        // For instance, Master and Worker are not related to a specific application.
+        // Only Driver and Executor set spark.app.id and spark.executor.id.
+        // Other instance types, e.g. Master and Worker, are not related to a specific application.
         val warningMsg = s"Using default name $defaultName for source because %s is not set."
         if (appId.isEmpty) { logWarning(warningMsg.format("spark.app.id")) }
         if (executorId.isEmpty) { logWarning(warningMsg.format("spark.executor.id")) }