[SPARK-5970][core] Register directory created in getOrCreateLocalRootDirs for automatic deletion.

As documented in createDirectory, the result of createDirectory is not registered for automatic removal. Currently there are 4 directories left in `/tmp` after just running `pyspark`.

Author: Milan Straka <[email protected]>

Closes #4759 from foxik/remove-tmp-dirs and squashes the following commits:

280450d [Milan Straka] Use createTempDir in getOrCreateLocalRootDirs...

Author: foxik

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

@@ -696,7 +696,7 @@ private[spark] object Utils extends Logging {
           try {
             val rootDir = new File(root)
             if (rootDir.exists || rootDir.mkdirs()) {
-              val dir = createDirectory(root)
+              val dir = createTempDir(root)
               chmod700(dir)
               Some(dir.getAbsolutePath)
             } else {