How to disable write ahead logs?

[Tim Harsch]

Hi all,
I set `spark.streaming.receiver.writeAheadLog.enable=false` and my history 
server confirms the property has been set.  Yet, I continue to see the error:

    16/11/28 15:47:04 ERROR util.FileBasedWriteAheadLog_ReceivedBlockTracker: 
Failed to write to write ahead log after 3 failures

I surmised from the spark users thread Spark Streaming Data loss on failure to 
write BlockAdditionEvent failure to WAL 
(https://www.mail-archive.com/user@spark.apache.org/msg58952.html) that HDFS 
append support must be enabled for WAL to work with HDFS.  My installation does 
not enable this HDFS feature, so I would like to disable WAL in Spark.

Thanks,
Tim