WebHdfsFileSystem should retry reads according to the configured retry policy.

In the current implementation of WebHdfsFileSystem, opens are retried according to the configured retry policy, but not reads. Therefore, if a connection goes down while data is being read, the read will fail and the read will have to be retried by the client code.

Also, after a connection has been established, the next read (or seek/read) will fail and the read will have to be restarted by the client code.