Request to add something like "Auth failed from IP" log report for built-in VNC server

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1828207
Reported by 'Druta Pavel' on 2019-05-08 :

In environment with needs of public accessible VNC ports there is no logs
or other registered events about authentication failures to analyze and/or
integrate it to automated services like fail2ban ans so on.
Thus the built-in VNC service is vulnerable to brutforce attacks and in
combination with weak built-in VNC-auth scheme can be a security
vulnerability.

Adding a simple log record like "QEMU VNC Authentication failed
192.168.0.5:5902 - 123.45.67.89:7898" will permit to quickly integrate it
to fail2ban system.