- Attempting to dump logfile groups using mysqldump led to a segmentation
  fault. mysqldump uses the `INFORMATION_SCHEMA.FILES` table to obtain
  information about logfile groups in order to produce the SQL statement
  required to create the logfile group. Previously the `EXTRA` column of
  the above table contained information about the node id and the undo
  buffer size of the logfile group. As part of adapting to the new design
  of the `FILES` table in 8.0, the decision was taken to remove this
  information since they were determined to be logfile group characteristics
  and not relevant to specific undo log files. However, as it turns out the
  undo buffer size is required by mysqldump in order to construct the
  CREATE LOGFILE GROUP statement
- Fix is to reintroduce the value of the undo buffer size in the `EXTRA`
  column of the `INFORMATION_SCHEMA.FILES` table

Change-Id: I0ccc79bccb30d27243277a03737b343cf99650a9