[SPARK-3979] [yarn] Use fs's default replication.

This avoids issues when HDFS is configured in a way that would not
allow the hardcoded default replication of "3".

Note: getDefaultReplication(Path) was added in 0.23.3, and the oldest
one available on Maven Central is 0.23.7, so I chose to not add code
to access that method via reflection.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #2831 from vanzin/SPARK-3979 and squashes the following commits:

b0e3a97 [Marcelo Vanzin] [SPARK-3979] [yarn] Use fs's default replication.

yarn/common/src/main/scala/org/apache/spark/deploy/yarn/ClientBase.scala

@@ -143,7 +143,8 @@ private[spark] trait ClientBase extends Logging {
     val nns = getNameNodesToAccess(sparkConf) + dst
     obtainTokensForNamenodes(nns, hadoopConf, credentials)
 
-    val replication = sparkConf.getInt("spark.yarn.submit.file.replication", 3).toShort
+    val replication = sparkConf.getInt("spark.yarn.submit.file.replication",
+      fs.getDefaultReplication(dst)).toShort
     val localResources = HashMap[String, LocalResource]()
     FileSystem.mkdirs(fs, dst, new FsPermission(STAGING_DIR_PERMISSION))