ddraw/tests: Skip cubemap tests when cubemap isn't supported.

[H. Verbeet]

2008/7/30 Stefan Dösinger <stefan at codeweavers.com>:
> DeviceLoadTest is quite big, does splitting up make sense? Otherwise, what
> you say is fair enough - I do not care too much about code beauty in the
> tests as long as the tests work(since one hardly ever reads the test or does
> lots of work on it, and the Windows apps we run are often crappy as well)
>
Please think of the poor people who are trying to fix driver bugs :-)