Java: Change in behavior of default value of MQEnvironment.userID

Change caused when using CLIENT transport for a channel not have a security exit defined.

From IBM® WebSphere® MQ 7.1, if an IBM WebSphere MQ classes for Java application is connecting to a queue manager, using the CLIENT transport through a channel that does not have a security exit defined, and the MQEnvironment.userID field is kept at its default value of the empty string ( ), the IBM WebSphere MQ classes for Java application queries the value of the Java System Property user.name and passes this to the queue manager for authorization as part of the MQQueueManager constructor.

If the user specified by the Java System Property user.name is not authorized to access the queue manager, the MQQueueManager constructor throws an MQException containing Reason Code MQRC_NOT_AUTHORIZED.