void fetchStarted() {
    // no-op for default output file
  }
Indicates that result fetching is started, and the converter should be activated. The
Converter starts to collect the data when the fetch is started, and prints out the
converted data when the fetch is finished. Converter will collect data only if
fetchStarted, and foundQuery is true.
beeline/src/java/org/apache/hive/beeline/OutputFile.java