[flare] Stop capturing the output when uncaught exceptions occur

Otherwise uncaught exceptions raised in a captured command
would make flare fail silently.

utils/flare.py

@@ -323,9 +323,12 @@ def _capture_output(self, command):
         backup_handlers = logging.root.handlers[:]
         logging.root.handlers = [logging.StreamHandler(out)]
         sys.stdout, sys.stderr = out, err
-        return_value = command()
-        sys.stdout, sys.stderr = backup_out, backup_err
-        logging.root.handlers = backup_handlers
+        try:
+            return_value = command()
+        finally:
+            # Stop capturing in a `finally` block to let uncaught exceptions be printed out
+            sys.stdout, sys.stderr = backup_out, backup_err
+            logging.root.handlers = backup_handlers
 
         return out, err, return_value