[DEPLOY] SPARK-3759: Return the exit code of the driver process

SparkSubmitDriverBootstrapper.scala now returns the exit code of the driver process, instead of always returning 0.

Author: Eric Eijkelenboom <ee@userreport.com>

Closes #2628 from ericeijkelenboom/master and squashes the following commits:

cc4a571 [Eric Eijkelenboom] Return the exit code of the driver process

core/src/main/scala/org/apache/spark/deploy/SparkSubmitDriverBootstrapper.scala

@@ -154,7 +154,8 @@ private[spark] object SparkSubmitDriverBootstrapper {
         process.destroy()
       }
     }
-    process.waitFor()
+    val returnCode = process.waitFor()
+    sys.exit(returnCode)
   }
 
 }