CDK-667: Initialize HDFS config in the FS Loader.

This fixes a bug where hdfs-site.xml is not loaded before attempting to
get a FileSystem for hdfs:/ URIs without the host and port, which should
be provided by the config.
Yes. We should probably use the other work-around, which is to call `FileSystem.getLocal(...)`, which seems to load `HdfsConfiguration`. I also think this might be a Hadoop bug if HdfsConfiguration is private.