Show the errors out. (#4305)

### What problem does this PR solve?


### Type of change

- [x] Refactoring

rag/raptor.py

                     ck_idx = [i + start for i in range(len(lbls)) if lbls[i] == c]
                     threads.append(executor.submit(summarize, ck_idx, lock))
                 wait(threads, return_when=ALL_COMPLETED)
+                for th in threads:
+                    if isinstance(th.result(), Exception):
+                        raise th.result()
                 logging.debug(str([t.result() for t in threads]))
 
             assert len(chunks) - end == n_clusters, "{} vs. {}".format(len(chunks) - end, n_clusters)

rag/svr/task_executor.py

             except Exception:
                 pass
             logging.debug("handle_task got TaskCanceledException", exc_info=True)
-        except Exception:
+        except Exception as e:
             with mt_lock:
                 FAILED_TASKS += 1
                 CURRENT_TASK = None
             try:
-                set_progress(task["id"], prog=-1, msg="handle_task got exception, please check log")
+                set_progress(task["id"], prog=-1, msg=f"[Exception]: {e}")
             except Exception:
                 pass
             logging.exception(f"handle_task got exception for task {json.dumps(task)}")