HDFS IO should comply with PTransform style guide

https://github.com/apache/beam/tree/master/sdks/java/io/hdfs/src/main/java/org/apache/beam/sdk/io/hdfs does not comply with https://beam.apache.org/contribute/ptransform-style-guide/ in a number of ways:

• It is not packaged as a PTransform (should be: HDFSIO.Read,Write or something like that)
• Should probably use AutoValue for specifying parameters

Stephen knows about the current state of HDFS IO.