tests: test the wl_display_roundtrip_queue() function
tests: test the wl_display_roundtrip_queue() function

[Pekka Paalanen: moved variable declarations to before code. Added some
comments, and added the re-arm to additionally test the opposite case.]

Signed-off-by: Pekka Paalanen <0f6ae7001e34c37b02fb2c1c2573ddf8f442136a@collabora.co.uk>

abooij/wayland,eyolfson/wayland,sir-murray/wayland,abooij/wayland,sir-murray/wayland,mchalupa/wayland,abooij/wayland,eyolfson/wayland,tulcod/wayland,mchalupa/wayland,bitfactor/wayland,tulcod/wayland,bitfactor/wayland,eyolfson/wayland,sir-murray/wayland,bitfactor/wayland,tulcod/wayland,mchalupa/wayland