Allow the setting of a Pyspark RDD's name attribute

This allows the setting of the underlying Java RDD's name attribute from python land.

```
In [2]: rdd = sc.parallelize(range(0, 10000))

In [3]: rdd.name = "cool"

In [4]: rdd.name
Out[4]: u'cool'
```

And after persisting:

![screen shot 2014-03-27 at 12 10 57 am](https://cloud.githubusercontent.com/assets/158950/2533730/6a8235e6-b566-11e3-8be9-841bb0d341a5.png)