tests: Add signal test case
tests: Add signal test case

Doesn't necessarily catch the signalfd bug just fixed, since that only
triggers when an uninitialized int is negative.

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