tests: roll out igt_fixture

tests: roll out igt_fixture

Also sprinkle igt_assert and igt_require over the setup code to clean
up code while at it. To avoid gcc getting upset about unitialized
variables just move them out of main as global data (where they always
get initialized to 0) - gcc can't see through our igt_fixture and
igt_subtest maze properly.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>