Use gvir_config_object_attach where appropriate
Use gvir_config_object_attach where appropriate

This allows us to properly refcount the underlying xmlDocPtr (and
the associated xmlNodes) to avoid trying to free twice the same
xmlNodes when disposing of GVirConfigObject referencing the same
nodes.

JGulic/libvirt-glib,JGulic/libvirt-glib,JGulic/libvirt-glib,JGulic/libvirt-glib,JGulic/libvirt-glib,libvirt/libvirt-glib,libvirt/libvirt-glib,libvirt/libvirt-glib