Setting the listen address for new domains to 0 is breaking libvirt's API standard, http://libvirt.org/formatdomain.html#elementsGraphics

Changed
lib/foreman/model/libvirt.rb#console:
vm.update_display(:password => password, :listen => '0')
to
vm.update_display(:password => password, :listen => '0.0.0.0')

The websocket still works (and starts working for existing systems), and virt-manager starts working again (For newly defined machines)

See pull request https://github.com/theforeman/foreman/pull/626