After many hours of trying to a get clean install virt-manager to run on my clean install kubuntu 18.04 (but guess it also applies to ubuntu 18.04) I found the fault is a syntax error in /etc/libvirt/qemu.conf line 412. It should be: group="kvm" and not: group=kvm. Once changed (under sudo) and running libvirtd -d and virt-manager under sudo I could finally get to create vm's.