[SPARK-4597] Use proper exception and reset variable in Utils.createT…

…empDir()

`File.exists()` and `File.mkdirs()` only throw `SecurityException` instead of `IOException`. Then, when an exception is thrown, `dir` should be reset too.

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes apache#3449 from viirya/fix_createtempdir and squashes the following commits:

36cacbd [Liang-Chi Hsieh] Use proper exception and reset variable.

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

@@ -262,7 +262,7 @@ private[spark] object Utils extends Logging {
         if (dir.exists() || !dir.mkdirs()) {
           dir = null
         }
-      } catch { case e: IOException => ; }
+      } catch { case e: SecurityException => dir = null; }
     }
 
     registerShutdownDeleteDir(dir)