commitlog_test: Add test for deadlock in shutdown w. segment wait
commitlog_test: Add test for deadlock in shutdown w. segment wait

Refs #8438

Ensures shutting down (well behaved) works even if an allocating
path is stuck waiting for a new segment - i.e. other aspect of

Closes #8475

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla