zkCli/ZooKeeperMain relies on system properties for TLS config

The command line client to ZooKeeper (org.apache.zookeeper.ZooKeeperMain, invoked via bin/zkCli.

) has no facility for accepting TLS client configuration (e.g. keystore/truststore location and password) except via system properties. System properties must be passed on the command line as "-D" arguments and are inherently not secure. There should be a way to pass the client TLS configuration to org.apache.zookeeper.ZooKeeperMain in a more secure way (e.g. via a file).