Fix return from handshake

Hi,

I noticed that after a handshake with a new peer, it never returned [here](https://github.com/OpenBazaar/OpenBazaar/blob/master/node/dht.py#L146), which I assume was intended, because it's here that peer info is added to the database.  I fixed this, but also removed the other lines that were there, because updating the routing table and adding to known nodes has already been done by that point.

Also included is a random bugfix for something I came across whilst breaking things - it now gives you the intended error message rather than a python complaint.

Thanks.