fix(connection): ensure connection cleanup before fallback retry

Now that we default to connecting to ipv6 hosts first, and then
fallback to ipv4, we need to make sure that there are no duplicate
event handlers attached to the connection which might cause
confusion up the chain.

lib/connection/connection.js

@@ -651,6 +651,13 @@ Connection.prototype.connect = function(_options) {
       );
     }
 
+    // clean up existing event handlers
+    this.connection.removeAllListeners('error');
+    this.connection.removeAllListeners('timeout');
+    this.connection.removeAllListeners('close');
+    this.connection.removeAllListeners('data');
+    this.connection = undefined;
+
     return doConnect(this, 4, _options, _errorHandler);
   });
 };