User joining with invalid PSK should see error

[holmesworcester]

In #1897 we began using libp2p private networks with a PSK for connection authentication. We get an error when the PSK is invalid but we are not displaying this to the user. We should!

If a user can connect to peers but gets rejected because of a PSK error, we should show that. However, the user should keep trying to connect to other peers, at least until all peers give the same error.

(Maybe the peer giving an error is in some incorrect state or has gone rogue.)

We can show this error in the connection startup sequence. "Invalid pre-shared key. Retrying."