Instead of using (only) a hard-coded list of VPN types,
prefer lookup the VPN settings from the .name files.
Still, fallback to a hard-coded list if the plugin cannot
be found, because for connection-add we currently don't
actually need the plugin installed.
OpenConnect needs three secrets - COOKIE, HOST and FINGERPRINT. They can be
obtained by authenticating to the server. This can be performed by running
"openconnect --authenticate <host>" and the three values are printed to stdout.
Note that the function may (probably will) interactively ask user for
his credentials.
Alternatively, it would be possible to dlopen() libopenconnect and call its
functions. However, as that would be more complicated and would also require
implementing functionality that openconnect simply does for free for us, it is
not worth it, I think.
