[MINOR] Add debug info to check the task num in executor (apache#506)

Author: colinmjj

core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala

@@ -190,7 +190,8 @@ private[spark] class CoarseGrainedExecutorBackend(
         exitExecutor(1, "Received LaunchTask command but executor was null")
       } else {
         val taskDesc = TaskDescription.decode(data.value)
-        logInfo("Got assigned task " + taskDesc.taskId)
+        logInfo(s"Got assigned task ${taskDesc.taskId}, " +
+          s"current executor running ${executor.runningTasks.size} tasks")
         taskResources.put(taskDesc.taskId, taskDesc.resources)
         executor.launchTask(this, taskDesc)
       }