Activate queue based router as default & Consider backend with no worker as unhealthy

[okayhooni]

There were valuable updates on routing logic with PrestoQueueLengthRoutingTable routing manager and PrestoQueueLengthChecker observer, like below.

• Presto Queue Length Based Routing Manager #81
• QueueBasedRouting: Use Running Count as fallback logic #173
• Add Support for User Queue Level Routing #176
• Filter out unhealthy clusters from queue based routing #183

But, current codebase in this repository don't use both PrestoQueueLengthRoutingTable and PrestoQueueLengthChecker. And besides, there is no option to activate those useful features without code modification.

I think, there is no reason to maintain HaRoutingManager as default, because PrestoQueueLengthRoutingTable is derived from it. So, it makes sense to activate PrestoQueueLengthRoutingTable and PrestoQueueLengthChecker by default.

Plus, I add minor logic to consider cluster with no worker as unhealthy.