Change the worker implementation to be buffered

[Supratim Samanta]

Currently, the workers are unbuffered. Any new task comes in, it will be started in a separate goroutine, so we are not really using the priority queue properly and there are stray goroutines in the background. If the system crashes, there will be many goroutines that will fail per worker. It the worker requests channel is buffered, we will have fewer failed tasks.

w := &Worker{ requests: make(chan *Request), pending: 0, index: i, Name: fmt.Sprintf("Worker-%d", i), done: b.done}