Auto-discovering ${top directory}/resources instead of
/usr/share/chaiwala-tests/resources means we don't have to depend
on the legacy chaiwala-tests package.

We still need to hard-code /usr/lib/apertis-tests to load the
LD_PRELOAD hack that we use to simulate a compromised pulseaudio
process, but we can reduce the test/fix cycle for the rest by
running it directly from a git checkout.

Reviewed-by: Philip Withnall <philip.withnall@collabora.co.uk>
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D4382