Merge pull request #583 from colorant/zookeeper.

Minor fix for ZooKeeperPersistenceEngine to use configured working dir

Author: Raymond Liu <raymond.liu@intel.com>

Closes #583 and squashes the following commits:

91b0609 [Raymond Liu] Minor fix for ZooKeeperPersistenceEngine to use configured working dir

(cherry picked from commit 68b2c0d02dbdca246ca686b871c06af53845d5b5)
Signed-off-by: Aaron Davidson <aaron@databricks.com>

Conflicts:
	core/src/main/scala/org/apache/spark/deploy/master/ZooKeeperPersistenceEngine.scala