Okay,
Jacob Wyatt gave the solution. Make sure that in /etc/libvirt/libvirtd.conf the line with "listen_tls = 0"
So
listen_tls = 0
becomes
# listen_tls = 0
Do this also in /config/etc/libvirt/libvirtd.conf this way you can safely reboot.
Tested this and my 2 nodes happily migrated a VM between them.
Michel