Fix undefined method scan issue
Fix undefined method scan issue

management_network_address was defaulting to UNSET_VALUE which is of
type Object, thus management_network_address was always truthy.

This fixes issue introduced in
e904fd8941249f9fefdac6fc43df6a3457f93139.

infernix/vagrant-libvirt,skamithi/vagrant-libvirt,brk3/vagrant-libvirt,electrofelix/vagrant-libvirt,mandre/vagrant-libvirt,electrofelix/vagrant-libvirt,infernix/vagrant-libvirt,electrofelix/vagrant-libvirt,pradels/vagrant-libvirt,Paulche/vagrant-libvirt,pradels/vagrant-libvirt,vagrant-libvirt/vagrant-libvirt,leoh0/vagrant-libvirt,sendgrid-ops/vagrant-libvirt,leoh0/vagrant-libvirt,vagrant-libvirt/vagrant-libvirt,swizzley/vagrant-libvirt,Paulche/vagrant-libvirt,swizzley/vagrant-libvirt,sendgrid-ops/vagrant-libvirt,brk3/vagrant-libvirt,skamithi/vagrant-libvirt,mandre/vagrant-libvirt,vagrant-libvirt/vagrant-libvirt,infernix/vagrant-libvirt