Should print all connection exceptions if connection fails

[jwiegley]

In Internal.hs, the following code tries all host/port combinations in series:

    connect ((host, port) : rest) = do
        ctx <- Conn.initConnectionContext
        result <- CE.try (Conn.connectTo ctx $ Conn.ConnectionParams
                              { Conn.connectionHostname  = host
                              , Conn.connectionPort      = port
                              , Conn.connectionUseSecure = tlsSettings
                              , Conn.connectionUseSocks  = Nothing
                              })
        either
            (\(ex :: CE.SomeException) -> do
                connect rest)
            (return)
            result
    connect [] = CE.throwIO $ ConnectionClosedException $ "Could not connect to any of the provided brokers: " ++ show (coServers connOpts)

Since this swallows all exceptions without printing them, if there's a deeper problem involved, the only thing the user will see is "Cannot connect to ", with no clue as to why. In my case, it was because I was missing netbase in my Ubuntu Docker image, so it wasn't a connection problem, but something much deeper (which the Exception clearly indicated).

I suggest capturing all these exceptions to a list, and if no connection is possible, print out the whole list, with each exception paired to the host/port that caused it.