core: sysvcompat - $network should be equivalent to network-online, rather than network target

Most likely the  facility needed is actual connectivity, rather than whether or not the
network managment daemon is running.

We also need to explicitly pull in the network-online.target, as it is not active by
default.

This means {systemd-networkd,NetworkManager}-wait-online.service, can be enabled by default
as part of network-online.target, and only delay boot when some service actively pulls it in.

See: <https://bugzilla.gnome.org/show_bug.cgi?id=728965>

Cc: Pavel Šimerda <psimerda@redhat.com>
Cc: Michal Sekletar <msekleta@redhat.com>
(cherry picked from commit 0404c609)