[SPARK-8320] [STREAMING] Add example in streaming programming guide that shows...

[SPARK-8320] [STREAMING] Add example in streaming programming guide that shows union of multiple input streams

Added python code to https://spark.apache.org/docs/latest/streaming-programming-guide.html
to the Level of Parallelism in Data Receiving section.

Please review and let me know if there are any additional changes that are needed.

Thank you.

Author: Neelesh Srinivas Salian <nsalian@cloudera.com>

Closes #6862 from nssalian/SPARK-8320 and squashes the following commits:

4bfd126 [Neelesh Srinivas Salian] Changed loop structure to be more in line with Python style
e5345de [Neelesh Srinivas Salian] Changes to kafak append, for loop and show to print()
3fc5c6d [Neelesh Srinivas Salian] SPARK-8320

docs/streaming-programming-guide.md

@@ -1937,6 +1937,14 @@ JavaPairDStream<String, String> unifiedStream = streamingContext.union(kafkaStre
 unifiedStream.print();
 {% endhighlight %}
 </div>
+<div data-lang="python" markdown="1">
+{% highlight python %}
+numStreams = 5
+kafkaStreams = [KafkaUtils.createStream(...) for _ in range (numStreams)]
+unifiedStream = streamingContext.union(kafkaStreams)
+unifiedStream.print()
+{% endhighlight %}
+</div>
 </div>
 
 Another parameter that should be considered is the receiver's blocking interval,