A running VM's page read its addresses while it rendered: the guest agent,
when its channel is connected but it does not answer, holds the page (and
a gunicorn worker) for its whole 10 s timeout, on every load. The page now
shows them once it has loaded: vm_addresses.js asks the new
instances/<pk>/addresses/ for each NIC's addresses and fills the header's
IPv4 and each network card's IPv4 and IPv6.
