1782 ERRRO

mysqlbinlog prints "ROLLBACK" at the end of binlog file. The ROLLBACK
caused the error that "@@SESSION.GTID_NEXT cannot be set to ANONYMOUS
when @@GLOBAL.GTID_MODE = ON."

It happened in below cases:
- Binlog file doesn't include any data related events.
  e.g. master-bin.1 only includes:
  Format_description_log_event
  Rotate_log_event

  and mysqlbinlog master-bin.1 master-bin.2 will output:
  BINLOG '... Format_description_log_event of master-bin.1...'
  ROLLBACK
  BINLOG '... Format_description_log_event of master-bin.2...'

- Relay log file includes a Format_description_log_event of master which
  is generated at starting server.
  e.g. the relay log includes:
  Format_description_log_event of relay log
  Format_description_log_event of master(generated when starting server)

  and mysqlbinlog output:
  BINLOG '... the binary of relay log's Format_description_log_event'
  ROLLBACK
  BINLOG '... the binary of master's Format_description_log_event'

When applying a Format_description_log_event, gtid_next's status will
be changed to NOT_YET_DETERMINDED_GROUP, so gtid_next will be decided
by the following event. If it is an Gtid_log_event, then it will be
set to gtid_next, otherwise ANONYMOUS is set. For above two cases,
It will set gtid_next to ANONYMOUS when applying ROLLBACK, but
gtid_mode is on, so it throws an error.

The fix has two parts:
- ROLLBACK is not printed out if there is no uncomplete transaction at the end
  of the binlog.
  SET @SESSION.GTID_NEXT = 'AUTOMATIC' is always printed at the end of each
  binlog, even the binlog is empty.
  It fixes the first case.

- Format_description_log_event of relay log is not output as a 'BINLOG'.
  it fixes the second case.