drm/i915/selftests: Skip live timeline/suspend tests if wedged

If the driver is wedged, we can not issue the requests to exercise the
timelines or the system across suspend, so skip the tests. live_hangcheck
is there to fail if we cannot recover.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190413125820.14112-4-chris@chris-wilson.co.uk