tests: use igt_exit() consistently with subtests

This is mostly important to get the SKIP reporting right, but I've
found a few stragglers that wanted to get converted over to the igt
result reporting completely.

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

tests/gem_ctx_bad_exec.c

@@ -126,5 +126,5 @@ int main(int argc, char *argv[])
 	igt_subtest("blt")
 		igt_assert(exec(fd, handle, I915_EXEC_BLT, ctx_id) != 0);
 
-	igt_success();
+	igt_exit();
 }