SPARK-3009: Reverted readObject method in ApplicationInfo so that Applic...

...ationInfo is initialized properly after deserialization

Author: Jacek Lewandowski <lewandowski.jacek@gmail.com>

Closes #1947 from jacek-lewandowski/master and squashes the following commits:

713b2f1 [Jacek Lewandowski] SPARK-3009: Reverted readObject method in ApplicationInfo so that ApplicationInfo is initialized properly after deserialization

core/src/main/scala/org/apache/spark/deploy/master/ApplicationInfo.scala

@@ -46,6 +46,11 @@ private[spark] class ApplicationInfo(
 
   init()
 
+  private def readObject(in: java.io.ObjectInputStream): Unit = {
+    in.defaultReadObject()
+    init()
+  }
+
   private def init() {
     state = ApplicationState.WAITING
     executors = new mutable.HashMap[Int, ExecutorInfo]