Re-raise Exception on debug mode

cliff/app.py

@@ -261,7 +261,7 @@ class App(object):
             subcommand = self.command_manager.find_command(argv)
         except ValueError as err:
             if self.options.debug:
-                LOG.exception(err)
+                raise
             else:
                 LOG.error(err)
             return 2

cliff/tests/test_app.py

@@ -379,3 +379,11 @@ def test_error_encoding_sys():
 def test_unknown_cmd():
     app, command = make_app()
     assert app.run(['hell']) == 2
+
+
+def test_unknown_cmd_debug():
+    app, command = make_app()
+    try:
+        app.run(['--debug', 'hell']) == 2
+    except ValueError as err:
+        assert "['hell']" in ('%s' % err)