LP #1724811: mysqld-systemd error when MySQL error-log doesn't exist in Centos/RHEL7

**Reported in Launchpad by Iwo last update 24-10-2017 06:45:21

If MySQL error-log doesn't exist a MySQL restart will cause mysqld-systemd to throw an error:

mysql-systemd[5691]: install: invalid user @MYSQLD_USER@

There's an unreplaced variable @MYSQLD_USER@ in mysqld-systemd script:

1. If log file is not specified it's put into datadir by default
   if [ ! -z $log ]; then
   if [ ! -e "$log" -a ! -h "$log" -a x$(dirname "$log") = "x/var/log" ]; then
   case $(basename "$log") in
   mysql*.log) install /dev/null -m0640 -o@MYSQLD_USER@ -g@MYSQLD_USER@ "$log" ;;
   *) ;;
   esac
   fi
   if [ -x /usr/sbin/restorecon ]; then
   [ -e "$log" ] && /usr/sbin/restorecon $log
   fi
   fi

The problem occurs only in PXC 5.7 (I've tested it against 5.7.19-29.22.1.el7) on Centos/RHEL 7.