compaction_manager: Return exception future in perform_cleanup
compaction_manager: Return exception future in perform_cleanup

We should return the exception future instead of throw a plain
exception.

Refs #6662

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