title: Enable _metadata files in Spark 2.1.0
body: <p>It seems that saving empty Parquet files is broken in Spark 2.1.0 as it is not possible to read them in again (due to faulty schema inference)</p>
  
  <p>I found that since Spark 2.0 writing the _metadata file is disabled by default when writing parquet files. But I cannot find the configuration setting to put this back on.</p>
  
  <p>I tried the following:</p>
  
  <pre><code>spark_session = SparkSession.builder \
                          .master(url) \
                          .appName(name) \
                          .config('spark.hadoop.parquet.enable.summary-metadata', 'true') \
                          .getOrCreate()
  </code></pre>
  
  <p>and quite some different combination as without <code>spark.hadoop</code> for example.</p>
  
  <p>The code I am trying to run in PySpark:</p>
  
  <pre><code>spark_session = session.get_session()
  sc = spark_session.sparkContext
  
  df = spark_session.createDataFrame(sc.emptyRDD(), schema)
  
  df.write.mode('overwrite').parquet(path, compression='none')
  
  # this works
  df = spark_session.read.schema(schema).parquet(path)
  
  # This throws an error
  df = spark_session.read.parquet(path)
  </code></pre>