add a randomization to the sleep and an integration spec for worker.rb

the way the threads work out currently is that 3 threads will spin up every 5 seconds and send 1000 points each, draining the queue.  This puts contention on the queue (thundering herd) and is probably less than ideal for sites that are hitting that 1000 max a lot.

randomizing the thread wake up should give a fairly even distribution of queue drains.

This also adds an integration spec for the queue.