Bugfix and Enhancements

Add a new listener for HTTP REST API (emqttd#1094) Fix the race condition issue caused by unregister_session/1 (emqttd#1096) Fix the issue that we cannot remove a down node from the cluster (emqttd#1100) Passed org.eclipse.paho.mqtt_sn.testing/interoperability tests (emq_sn#29) Fixed the issue that send http request and return non-200 status code, but AUTH/ACL result is denied (emq-auth-http#33) Fixed the issue that fail to stop listener (emq_stomp#24) Support using systemctl to manage emqttd service on CentOS