Testconfig: Added winrt stage for qtbase#dev

Added winrt-x64-msvc2012_Windows_8 stage for QtBase_dev_Integration
project.

Change-Id: I1b5b561352a6512ee0380684de99e7f4f0c28e3d
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Tony Sarajärvi <tony.sarajarvi@digia.com>