SPARK-1158: Fix flaky RateLimitedOutputStreamSuite.

There was actually a problem with the RateLimitedOutputStream implementation where the first second doesn't write anything because of integer rounding.

So RateLimitedOutputStream was overly aggressive in throttling.

Author: Reynold Xin <rxin@apache.org>

Closes #55 from rxin/ratelimitest and squashes the following commits:

52ce1b7 [Reynold Xin] SPARK-1158: Fix flaky RateLimitedOutputStreamSuite.
Remove broken/unused Connection.getChunkFIFO method.

This method appears to be broken -- since it never removes
anything from messages, and it adds new messages to it,
the while loop is an infinite loop.  The method also does not appear
to have ever been used since the code was added in 2012, so
this commit removes it.

cc @mateiz who originally added this method in case there's a reason it should be here! (https://github.com/apache/spark/commit/63051dd2bcc4bf09d413ff7cf89a37967edc33ba)

Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes #69 from kayousterhout/remove_get_fifo and squashes the following commits:

053bc59 [Kay Ousterhout] Remove broken/unused Connection.getChunkFIFO method.