util-app: Fetch networking info too
util-app: Fetch networking info too

On creating the libvirt system connection, also fetch info on networks
managed by this connection along with domains.

This will be needed by the following patches to get the IP address of
guest.

https://bugzilla.gnome.org/show_bug.cgi?id=744004

vbenes/gnome-boxes,vbenes/gnome-boxes