tests: disable reactor stall notifier
tests: disable reactor stall notifier

In case it is interacting badly with ASAN and causing spurious test
failures.

scylladb/scylla,duarten/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla