fix/remove incorrect add_known_node() call

this should be (uri, pubkey, guid, nickname) but add_peer() will call
add_known_node() anyway, so just remove this call

Signed-off-by: Thomas Stilwell <stilwellt@openlabs.co>
make DHT::add_known_node() private

Signed-off-by: Thomas Stilwell <stilwellt@openlabs.co>
Merge pull request #865 from benemorius/fix-add-knownnodes-call

fix/remove incorrect add_known_node() call