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

[Stefan Dösinger]

> There are some tests after that block not related to cubemap which I
> don't want
> to skip. Other options are moving cubemap block of code to the end (so
> that I
> can return then) or skipping the block by goto, but none of this are
> really
> better IMO.
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)