runner/job_list: return error on crashes while running --list-subtests

Changes on tests may break --list-subtests, if they, for instance,
someone adds a code outside igt_subtests that depends on igt_fixture
to run, causing:

        Received signal SIGABRT.
        Stack trace:
         #0 [fatal_sig_handler+0x17b]
         #1 [__sigaction+0x50]
         #2 [__pthread_kill_implementation+0x10c]
         #3 [gsignal+0x16]
         #4 [abort+0xd7]
         #5 [__assert_fail_base.cold+0xf]
         #6 [__assert_fail+0x46]
         #7 [internal_assert+0xe5]
         #8 [igt_fail+0xea]
         #9 [__igt_fail_assert+0x10e]
         #10 [xe_number_hw_engines+0x6b]
         #11 [__igt_unique____real_main1528+0x1ac0]
         #12 [main+0x23]
         #13 [__libc_start_call_main+0x80]
         #14 [__libc_start_main+0x89]
         #15 [_start+0x25]
        Aborted (core dumped)

IGT runner currently prints the message, but don't ignore the
error. That prevents scripts to rely on the IGT testlist
output, as the list will miss subtests.

So, instead, return an error.

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org>