Investigate YARN placement.

While running a 3 day webindex test I noticed that YARNs placement of task was not always ideal. For example with 20 nodes, I created 20 workers task. However sometimes YARN may place 2 worker task on a single node because another node had the Oracle.

Thinking about this, maybe I should have created 19 worker task and given the Oracle and Twill coordinator task their own nodes. However, not sure how to make YARN do this.