'Creates a new gzipped output tempfile for the output type.
We write to JSON data to gzip_filehandle to get compressed data. We hold a
reference to the original filehandle (gzip_filehandle_parent) so we can pass
the gzip data to bigquery.
Args:
output_type: string of export type to be used in filename. e.g.
ExportedFile
Returns:
A TempOutputTracker object'

def _CreateOutputFileHandles(self, output_type):

    gzip_filehandle_parent = tempfile.NamedTemporaryFile(suffix=output_type)
    gzip_filehandle = gzip.GzipFile(gzip_filehandle_parent.name, 'wb', self.GZIP_COMPRESSION_LEVEL, gzip_filehandle_parent)
    self.temp_output_trackers[output_type] = TempOutputTracker(output_type=output_type, gzip_filehandle=gzip_filehandle, gzip_filehandle_parent=gzip_filehandle_parent)
    return self.temp_output_trackers[output_type]
