Use xdg-shell in tests

[Marek Chalupa]

Hi,

in this series of patches I added support for xdg-shell/surface
to the test-suite.

The thing that led me to this is captured in the last patch, that is
that maximizing and fullscreening didn't work as expected for really
simple client (just bare xdg-surface and nothing more). However, I'm
not sure if that was error in client or bug in weston, so I created
this tests and I'd like to ask you for review - maybe it's really bug,
maybe I've just forgotten something.

Thanks,
Marek