Console warning on WSS close

[grctest]

When a websocket is closed, an error message is logged in the console:

undefined
error: wss connection closed

This is because of the following lines in the ChainWebSocket:

 // in onClose function:

    for (var cbId = this.responseCbId + 1; cbId <= this.cbId; cbId += 1) {
      this.callbacks[cbId].reject("wss connection closed");
    }

  .......

  login = (user, password) => this.connect_promise.then(() => this.call([1, "login", [user, password]]));

So we could change the onClose function to avoid throwing an error on WSS closure. Resolving instead of rejecting isn't an option neither.

Upside is this isn't blocking, just cosmetic.