producer.send with sync_publish=true set against activemq blocks and doesn't return

While producer.send with system property sync_publish=true against activemq block failing to return, the same scenario works fine against Microsoft Azure Service Bus.

This interferes with testing isolated local systems without remote MS ASB integration.

This was not tested against either of the Qpid brokers or the Active MQ 5.9.0 codebase.