exhaustive custom cluster tests never run

While investigating IMPALA-3614 I found another problem: there are a few tests, including all of breakpad, that are set to run with exhaustive exploration strategy only. Well, they're not being run even there:

custom_cluster/test_admission_controller.py .....
custom_cluster/test_alloc_fail.py ..
custom_cluster/test_breakpad.py ssss

I think the problem is the exploration strategy option in run-all-tests.sh never gets passed correctly to run-custom-cluster-tests.sh