Rewrite nm-online to use libnm-glib, and change it so that it waits
until NM has finished all of its startup-time connection activation
attempts, rather than only waiting until at least one has succeeded.

In particular, this means that on multi-homed servers, the
NetworkManager-wait-online systemd service (and by extension,
network.service) will now block until *all* of the server's IP
addresses are up, which is needed for some old daemons that assume
that no network interfaces will be added after they start.