message: Show login error message returned from back-end
  Show in login screen the error that the back-end is outputting to better inform to the user what went wrong.
  Fixes kiali/kiali#3150
diff: @@ -36,7 +36,10 @@ const loginState = (state: LoginStateInterface = INITIAL_LOGIN_STATE, action: Ki
  case getType(LoginActions.loginFailure):
  let message = 'Error connecting to Kiali';
  - if (action.payload.error.request.status === 401) {
  + const response_data = action.payload.error.response.data;
  + if (response_data && typeof response_data.error == 'string' && response_data.error.length > 0) {
  + message = `Login unsuccessful: ${response_data.error}`;
  + } else if (action.payload.error.response.status === 401) {
  message =
  'Unauthorized. The provided credentials are not valid to access Kiali. Please check your credentials and try again.';
  }
  