meson: IVI plugin tests do not use config

If Weston is not installed, running ivi-layout test would fail on lots of image
files not found which presumably causes the creation of some ivi surfaces to
fail, leading to an assert failure.

Looking at the test setup in weston-tests-env, these IVI plugin tests are
supposed to run with --no-config instead.

Fixes: https://gitlab.freedesktop.org/wayland/weston/issues/195



Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>