WinRT: Fix QSettings auto-tests

WinRT is a sanboxed environment, hence files can only be created in
some writable location.
For some tests we reset the current directory to minimize the required
changes. We cannot do this for the application lifetime as the test
also has cases where it reads files relative to the executable inside
the sandbox.

Change-Id: Ib9d37c8cffd191f0d1055f835c11d10887923378
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
WinRT: Do not forget the path specification

The path value can be used to access any container or subcontainer
in the settings, even if it is not created by Qt.

Change-Id: I431d8a8b129dafb4ec85227421dc37ec76c18ecf
Reviewed-by: Andrew Knight <andrew.knight@digia.com>