Zookeeper SSL/TLS support

Zookeeper 3.5.5 server can operate with SSL/TLS secure connection with its clients.

https://cwiki.apache.org/confluence/display/ZOOKEEPER/ZooKeeper+SSL+User+Guide

The SSL communication should be possible in the different parts of YARN, where it communicates with Zookeeper servers. The Zookeeper clients are used in the following places:

• ResourceManager
• ZKConfigurationStore
• ZKRMStateStore

The yarn.resourcemanager.zk-client-ssl.enabled flag to enable SSL communication should be provided in the yarn-default.xml and the required parameters for the keystore and truststore should be picked up from the core-default.xml (HADOOP-18709)

yarn.resourcemanager.ha.curator-leader-elector.enabled has to set to true via yarn-site.xml to make sure Curator is used, otherwise we can't enable SSL.