[SPARK-4597] Use proper exception and reset variable in Utils.createTempDir()

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

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

(cherry picked from commit 49fe8797e64f10c574e0790b32a8c3fdc7e594a0)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>