Comment 7 for bug 1574168

Did you also see the specific error message "Can't create database 'performance_schema'; database exists" ?

We saw this when upgrading from Ubuntu 14.04 to 16.04 due to a race condition between the new postinst and old upstart script (which would still be running until the host is rebooted and switched to systemd).

This was fixed as per https://bugs.launchpad.net/ubuntu/+source/mysql-5.7/+bug/1577712 (not yet released), but if you're still seeing the same issue after a reboot then it might be a separate problem.