QtIFW

Fix focus handling on the FinishedPage

Simplify entering() / leaving() implementation for wizard pages,
above methods are now called a bit later, when the new page is
already visible. Calling setFocus() inside entering() should
work properly right now.

Change-Id: Ic5d194f074cc4b1fc419c7be70563e105e644957
Reviewed-by: Niels Weber <niels.weber@theqtcompany.com>