At various places, nmcli requires to specify a VPN type by name, for example
$ nmcli connection add type vpn ifname '*' vpn-type $VPN_TYPE
This $VPN_TYPE used to be a hard-coded list of known VPN plugin names.
But actually, it should be a VPN service-type. A service-type used to be
the D-Bus name of the VPN plugin. Now, with multiple VPN support that
is no longer the case, but it still has the form of a D-Bus bus name.
Alternativley, it could be an alias, which is just a way for plugins
to support multiple service-types.
Fix that, to support fully qualified service-types in the form
of D-Bus bus names. Also, support lookup by name, in which case
the present plugin-info instances are searched.
Finally, support a list of hard-code short-names.
All the logic how to translate a short-name to a fully qualified
service-type is now inside libnm, so that various user agree on
those names and don't have to hard-code them each.
4cb57964d9