tests: fix a race condition in ivi-shell tests

tests: fix a race condition in ivi-shell tests

ivi-shell tests load their own controller plugin
for testing purposes. Tests also uses the generated
weston-ivi.in config file, which causes weston to
load hmi-controller and its helper client.
Existence of hmi-controller and its helper client
confuses test plugins. Because they are creating
surfaces and layers which are not expected by
test plugins.

We can start ivi-shell tests without config file
to solve this problem. Then, weston will not load
hmi-controller plugin.

Reported-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Signed-off-by: Emre Ucan <eucan@de.adit-jv.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Acked-by: Daniel Stone <daniels@collabora.com>