They're causing troubles because this runs all the igt_fixtures, and
doing that on a build machine is at best surprising.

The main aim for this is catching testcases which fail to call
igt_exit. But just enumerating subtests does that too, and we have
library unit tests to make sure that's the case (with igt_no_exit and
igt_no_exit_list_only).

Cc: Petri Latvala <petri.latvala@intel.com>
Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Reviewed-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>