@ModuleOption("the username to use when connecting to the broker")
	public void setUsername(String username) {
		this.username = username;
	}
Factors out common options about configuring a connection to an MQTT broker.

@author Eric Bottard
@author Gary Russell
spring-xd-dirt/src/main/java/org/springframework/xd/dirt/modules/metadata/MqttConnectionMixin.java