Currently nmcli considers the state of the device associated to a
connection to determine the success of an activation; for VPNs the
device is the parent interface on which the VPN is established.
This means that VPNs on bond/bridge/team interfaces are reported as
connected immediately because of the special handling of master
devices state in check_activated().
The parent device state is not meaningful for VPNs, so don't track it.