* Allow the logback directory for ETL jobs to be overridden using system property.
See https://logback.qos.ch/manual/configuration.html#variableSubstitution for more details.
* Add WHZ_ETL_TEMP_DIR env var and play config to control where the ETL job logs & temp files to be saved.
This enables us to move away from the default /var/tmp/wherehows directory.