[SPARK-1037] The name of findTaskFromList & findTask in TaskSetManager.scala is confusing

Hi all - I've renamed the methods referenced in this JIRA to clarify that they modify the provided arrays (find vs. deque).

Author: Ilya Ganelin <ilya.ganelin@capitalone.com>

Closes #3665 from ilganeli/SPARK-1037B and squashes the following commits:

64c177c [Ilya Ganelin] Renamed deque to dequeue
f27d85e [Ilya Ganelin] Renamed private methods to clarify that they modify the provided parameters
683482a [Ilya Ganelin] Renamed private methods to clarify that they modify the provided parameters