An initial stab at an RDD for Variant Store.

The Variant and Read classes have a complex hierarchy all the way up to map, I think that's why the method invocation is done explicitly on the Reads example.

```
java.util.AbstractMap<java.lang.String,java.lang.Object>
  com.google.api.client.util.GenericData
    com.google.api.client.json.GenericJson
      com.google.api.services.genomics.model.Variant
```