Stuff finally works!
What I did was.
Removed everything ovirt-related:
# yum remove \*ovirt\* \*vdsm\* \*libvirt\*
# reboot
Installed 3.6 from scratch:
# yum install
http://resources.ovirt.org/pub/yum-repo/ovirt-release36.rpm
# yum install ovirt-engine
Restored backup:
# su - postgres
# psql -d template1 -c "create database engine owner engine;
# engine-backup --mode=restore restore-permissions --provision-db
--provision-dwh-db --provision-reports-db --file=engine-backup.tar.gz
--log=engine-backup-restore.log
Now I'm back to working 3.6
Updating to 4.0
# yum install
http://resources.ovirt.org/pub/yum-repo/ovirt-release40.rpm
# yum update "ovirt-engine-setup*"
# engine-setup
Cheers
Marcin.