libvirt-machine-properties: Save machine's name on change
libvirt-machine-properties: Save machine's name on change

This patch ensures that the machine's name is saved everytime it changes.

Also, together with following patches this allows editing name through
window's title.

https://bugzilla.gnome.org/show_bug.cgi?id=692383

vbenes/gnome-boxes,vbenes/gnome-boxes