vpn-select: Demand hood file to be provided as argument

By removing the reference to the hood file from vpn-select, we
remove the entire dependency from fff-hoodutils.
vpn-select will now work with any file provided, as long as
it has the correct syntax. At the moment, the only provider
is the configurehood script. Since the various hood file variants
are handled there, it seems logical that configurehood also
chooses and provides the correct hood file for vpn-select, instead
of vpn-select which had no other contact with hood file choice.

This is simple, tidy and effective.

Adjusted some comments.

Fixes #106

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Robert Langhammer <rlanghammer@web.de>
Reviewed-by: Fabian Bläse <fabian@blaese.de>