To enable some different test cases such as:
- filling/draining the broker.
- measuring the time to consume messasges with a backlog whilst messages are being published.
1) Augment Testing framework to take a 'preFill' value which is some value of messages that will be sent to the broker before the test cycle begins.
2) Add a 'delayBeforeConsume' value that provides a time (in ms) to wait after having pre-filled the broker before the consumers are started.
3) Update the tests to allow 0 value for numConsumers meaning no consumers.
4) Add ability to skip message sending, consumeOnly=true.
These changes will allow us to pre-fill the broker with data to test the performance with a full heap.
Documentation of new features should be added to performance test page.