I've followed your link, from my notes I see I've already tested it in
 the beginning of my messing. I've set 'ssl = false' in
/etc/vdsm/vdsm.conf and run 'vdsm-tool configure --force'. Since it
has just commented out 'spice_tls=1', I've forced it to 'spice_tls=0'
(though it should give the same result as commenting out) and run once
 again 'vdsm-tool configure --force'.

There was no warning report about non-configured stuff. Vdsm still
fails to start.

I've attached 2 logs, compressed in one archive 'vdsm_logs.xz'.

These logs are:

1) vdsmd_journalctl.0.txt contains the result of
'journalctl -xe -u vdsmd'

2) vsdm_messages_err.1.txt contains the result of
'grep -i vdsm /var/log/messages'

Quick summary with what I think are the relevant lines from the logs:
# journalctl -xe -u vdsmd
[...]
Nov 06 14:18:28 onode1.ifac.cnr.it vdsmd_init_common.sh[18732]: vdsm: Running tune_system
Nov 06 14:18:28 onode1.ifac.cnr.it vdsmd_init_common.sh[18732]: sysctl: cannot stat /proc/sys/ssl: No such file or directory
Nov 06 14:18:28 onode1.ifac.cnr.it systemd[1]: vdsmd.service: control process exited, code=exited status=1
Nov 06 14:18:28 onode1.ifac.cnr.it systemd[1]: Failed to start Virtual Desktop Server Manager.
[...]

# grep -i vdsm /var/log/messages
[...]
Nov  6 14:24:59 onode1 vdsmd_init_common.sh: vdsm: Running tune_system
Nov  6 14:24:59 onode1 vdsmd_init_common.sh: sysctl: cannot stat /proc/sys/ssl: No such file or directory
Nov  6 14:24:59 onode1 vdsmd_init_common.sh: vdsm: stopped during execute tune_system task (task returned with error code 255).
Nov  6 14:24:59 onode1 systemd: vdsmd.service: control process exited, code=exited status=1
Nov  6 14:24:59 onode1 systemd: Dependency failed for MOM instance configured for VDSM purposes.
Nov  6 14:24:59 onode1 systemd: Job mom-vdsm.service/start failed with result 'dependency'.
Nov  6 14:24:59 onode1 systemd: Unit vdsmd.service entered failed state.
Nov  6 14:24:59 onode1 systemd: vdsmd.service failed.
Nov  6 14:25:00 onode1 systemd: vdsmd.service holdoff time over, scheduling restart.
[...]

I can't find anything on Google and in oVirt documentation regarding
these issues.