[STREAMING] SPARK-2343: Fix QueueInputDStream with oneAtATime false

Fix QueueInputDStream which was not removing dequeued items when used with the oneAtATime flag disabled.

Author: Manuel Laflamme <manuel.laflamme@gmail.com>

Closes #1285 from mlaflamm/spark-2343 and squashes the following commits:

61c9e38 [Manuel Laflamme] Unit tests for queue input stream
c51d029 [Manuel Laflamme] Fix QueueInputDStream with oneAtATime false