drm/i915/selftests: Include the subsubtest name for live_parallel_engines

Include the name of the failing subsubtest, should it fails.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191123191547.925360-1-chris@chris-wilson.co.uk