Ensure that files are fetched atomically

tempFile is created in the same directory than targetFile, so that the
move from tempFile to targetFile is always atomic

Author: Christophe Préaud

core/src/main/scala/org/apache/spark/util/Utils.scala

@@ -425,8 +425,7 @@ private[spark] object Utils extends Logging {
       conf: SparkConf,
       securityMgr: SecurityManager,
       hadoopConf: Configuration) {
-    val tempDir = getLocalDir(conf)
-    val tempFile = File.createTempFile("fetchFileTemp", null, new File(tempDir))
+    val tempFile = File.createTempFile("fetchFileTemp", null, new File(targetDir.getAbsolutePath))
     val targetFile = new File(targetDir, filename)
     val uri = new URI(url)
     val fileOverwrite = conf.getBoolean("spark.files.overwrite", defaultValue = false)