title: React Native navigating between Nested StackNavigator
body: <p>I have the three navigators below, I am navigating to the DashBoard Screen after the login is completed but I have an issue when I want to logout from the DashBoard Screen, <strong>this.props.navigation.navigate('Login')</strong> is working fine but I want to clear the stack when signout button is pressed. </p>
  
  <pre><code>const DashBoardStackNavigator = createStackNavigator({
        DashBoard: DashBoard,
        Second:Second,
        Third:Third
      })
  
  
  const BottomTabNavigator = createBottomTabNavigator({
    DashBoardStackNavigator,
    Account,
    Report,
    Members
  }})
  
  const AppStackNavigator = createStackNavigator({
    Login: Login,
    BottomTabNavigator: BottomTabNavigator
  
  })
  
  
  export default createAppContainer(AppStackNavigator)
  </code></pre>
  
  <p>I tried the following with no luck</p>
  
  <pre><code>const resetAction = StackActions.reset({
    index: 0,
    actions: [NavigationActions.navigate({ routeName: 'Login' })],
  });
  this.props.navigation.dispatch(resetAction);
  </code></pre>
  
  <blockquote>
    <p>Error: there is no route defined for key Login, Must Be one of
    DashBoard</p>
  </blockquote>