LP #1651505: GTID position not recorded when --binlog-info=AUTO

**Reported in Launchpad by Jericho Rivera last update 20-06-2017 08:07:54

Since PXB 2.3.2 and 2.4.x, when taking a backup using xtrabackup binary (eg in v2.4.5) instead of innobackupex the GTID position is not recorded unless you specify --binlog-info=ON during backup phase.

1. cat xtrabackup/xtrabackup_binlog_info
   mysql-bin.000009 194

1. cat xtrabackup/xtrabackup_info
   uuid = 5b6db0a4-c6cb-11e6-807f-00163e7d7303
   name =
   tool_name = xtrabackup
   tool_command = --user=root --password=... --backup --target-dir=/root/backups/xtrabackup/
   tool_version = 2.4.5
   ibbackup_version = 2.4.5
   server_version = 5.7.16-10-log
   start_time = 2016-12-20 15:45:37
   end_time = 2016-12-20 15:45:39
   lock_time = 0
   binlog_pos =
   innodb_from_lsn = 0
   innodb_to_lsn = 252679027
   partial = N
   incremental = N
   format = file
   compact = N
   compressed = N
   encrypted = N

PXB defaults to --binlog-info=AUTO based on the manual - https://www.percona.com/doc/percona-xtrabackup/2.4/advanced/lockless_bin-log.html.

During the prepare phase, xtrabackup creates the xtrabackup_binlog_info file but it does not have the GTID coordinates needed to setup replication on the slave.

How to repeat:

• Setup master 5.7.16 with GTID enabled
• execute `xtrabackup --backup --target-dir=/path`
• check `xtrabackup_info` and `binlog_pos=` line is empty
• run `xtrabackup --prepare --target-dir=path`, `xtrabackup_binlog_info` is created but no GTID coordinates

• do the same but use `innobackupex /path`, from the onset you'll see that `binlog_pos=` is populated in `xtrabackup_info` file and `xtrabackup_binlog_info` has proper GTID coordinates.

Not sure if this is a doc issue where we should notify users to use --binlog-info=ON when taking backups from GTID based servers or needs a code fix.