Make nova-manage emit a traceback when things blow up

If we hit an unhandled error in nova-manage we don't
get a traceback currently which makes debugging the actual
failure hard. This change emits a traceback in main() when
we get an unhandled exception up from one of the subcommands.

Change-Id: Id8b8ad3c97c6834abc4290319cd6f2cd5aafa479
Related-Bug: #1650694

nova/cmd/manage.py

@@ -57,6 +57,7 @@
 import functools
 import os
 import sys
+import traceback
 
 import decorator
 import netaddr
@@ -1583,6 +1584,6 @@ def main():
         ret = fn(*fn_args, **fn_kwargs)
         rpc.cleanup()
         return(ret)
-    except Exception as ex:
-        print(_("error: %s") % ex)
+    except Exception:
+        print(_("An error has occurred:\n%s") % traceback.format_exc())
         return(1)

nova/tests/unit/test_nova_manage.py

@@ -1410,3 +1410,24 @@ def test_validate_transport_url_favors_command_line(self):
         from_cli = 'fake://otheruser:otherpass@otherhost:otherport'
         self.assertEqual(from_cli,
                          self.commands._validate_transport_url(from_cli))
+
+
+class TestNovaManageMain(test.NoDBTestCase):
+    """Tests the nova-manage:main() setup code."""
+
+    def setUp(self):
+        super(TestNovaManageMain, self).setUp()
+        self.output = StringIO()
+        self.useFixture(fixtures.MonkeyPatch('sys.stdout', self.output))
+
+    @mock.patch.object(manage.config, 'parse_args')
+    @mock.patch.object(manage, 'CONF')
+    def test_error_traceback(self, mock_conf, mock_parse_args):
+        with mock.patch.object(manage.cmd_common, 'get_action_fn',
+                               side_effect=test.TestingException('oops')):
+            self.assertEqual(1, manage.main())
+            # assert the traceback is dumped to stdout
+            output = self.output.getvalue()
+            self.assertIn('An error has occurred', output)
+            self.assertIn('Traceback', output)
+            self.assertIn('oops', output)