fix(show_alive_threads): make it safe
fix(show_alive_threads): make it safe

inspect routines we are using can raise Exceptions in some cases
lets catch and log them, and return placeholder in such case

scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests