LP #1738383: xtrabackup won't run when slave_parallel_workers > 0 and --slave-info is used

**Reported in Launchpad by Rick Pizzi last update 15-12-2017 09:36:11

In case of a multi threaded slave, xtrabackup refuses to run if --slave-info option is used.

However, as per this upstream bug http://bugs.mysql.com/bug.php?id=74528 it has been demonstrated that it is safe to trust exec_master_log_pos with MTS, if the slave SQL thread is stopped before taking the backup.

Following that, I expected --slave-info to be accepted if --safe-slave-backup is also used, but apparently, xtrabackup just refuses to run if the variable slave_parallel_workers has a value greater than zero and --slave-info is used, no matter the other options I use.

xtrabackup version 2.4.9 based on MySQL server 5.7.13 Linux (x86_64) (revision id: a467167cdd4)