I tried ignore-db-dir=lost+found but it didn't work, in 5.7.14 path to the default datadir /var/lib/mysql is also coded in /usr/share/mysql/mysql-systemd-start as MYSQLDATA=/var/lib/mysql changing this variable worked for me. Hope this helps.
I tried ignore- db-dir= lost+found but it didn't work, in 5.7.14 path to the default datadir /var/lib/mysql is also coded in /usr/share/ mysql/mysql- systemd- start as MYSQLDATA= /var/lib/ mysql
changing this variable worked for me. Hope this helps.