Spark Integration: SparkPageRank now uses Service

Added a simple service to SparkPageRank example application to showcase how to use services in Spark.

@anew : Please review. Thanks.
The cleaner way is to use a double try.

```java
try {
  BufferedReader reader = new BufferedReader(...);
  try {
    .....
  } finally {
    Closeables.closeQuietly(reader);
  }
} catch (Exception e) {
  LOG.error("....", e);
  throw Throwables.propagate(e);
}
```