lib: make igt_set_vt_graphics_mode never fail

All tests agree that this is a letal failure, so no point
to pass it back to callers.

Also add some igt_require calls for the drm_fd where I've
noticed that it's missing.

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

tests/kms_setmode.c

@@ -702,7 +702,7 @@ int main(int argc, char **argv)
 	igt_fixture {
 		drm_fd = drm_open_any();
 		if (!dry_run)
-			do_or_die(igt_set_vt_graphics_mode());
+			igt_set_vt_graphics_mode();
 
 		drm_resources = drmModeGetResources(drm_fd);
 		assert(drm_resources);