[SPARK-12142][CORE]Reply false when container allocator is not ready and reset target

Using Dynamic Allocation function, when a new AM is starting, and ExecutorAllocationManager send RequestExecutor message to AM. If the container allocator is not ready, the whole app will hang on

Author: meiyoula <1039320815@qq.com>

Closes #10138 from XuTingjun/patch-1.

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

@@ -370,6 +370,7 @@ private[spark] class ExecutorAllocationManager(
     } else {
       logWarning(
         s"Unable to reach the cluster manager to request $numExecutorsTarget total executors!")
+      numExecutorsTarget = oldNumExecutorsTarget
       0
     }
   }

yarn/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMaster.scala

@@ -600,11 +600,12 @@ private[spark] class ApplicationMaster(
               localityAwareTasks, hostToLocalTaskCount)) {
               resetAllocatorInterval()
             }
+            context.reply(true)
 
           case None =>
             logWarning("Container allocator is not ready to request executors yet.")
+            context.reply(false)
         }
-        context.reply(true)
 
       case KillExecutors(executorIds) =>
         logInfo(s"Driver requested to kill executor(s) ${executorIds.mkString(", ")}.")