tests: add one more test for event-loop signal source
tests: add one more test for event-loop signal source

Test if when we get a signal, all signal sources for that signal
get dispatched.

Signed-off-by: Marek Chalupa <a05df156a69ad59faa9af9b666ef78009594c145@gmail.com>
Reviewed-by: Pekka Paalanen <0f6ae7001e34c37b02fb2c1c2573ddf8f442136a@collabora.co.uk>

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