nova-status: return 255 for unexpected errors

This came up during review of I687dd7317703a1bb76c197ebba849ca368c0872e.

Change-Id: I2dd62e994957d4cc8cc4a8b23a604b03815f2639

doc/source/man/nova-status.rst

@@ -61,14 +61,16 @@ Upgrade
   service catalog.
 
   **Return Codes**
+    ::
 
-  0) All upgrade readiness checks passed successfully and there is nothing
-     to do.
-  1) At least one check encountered an issue and requires further
-     investigation. This is considered a warning but the upgrade may be OK.
-  2) There was an upgrade status check failure that needs to be
-     investigated. This should be considered something that stops an
-     upgrade.
+    0) All upgrade readiness checks passed successfully and there is nothing
+       to do.
+    1) At least one check encountered an issue and requires further
+       investigation. This is considered a warning but the upgrade may be OK.
+    2) There was an upgrade status check failure that needs to be
+       investigated. This should be considered something that stops an
+       upgrade.
+    255) An unexpected error occurred.
 
   **History of Checks**
 

nova/cmd/status.py

@@ -205,5 +205,5 @@ def main():
         return(ret)
     except Exception:
         print(_('Error:\n%s') % traceback.format_exc())
-        # This is 10 so it's not confused with the upgrade check exit codes.
-        return 10
+        # This is 255 so it's not confused with the upgrade check exit codes.
+        return 255

nova/tests/unit/cmd/test_status.py

@@ -74,7 +74,7 @@ class TestNovaStatusMain(test.NoDBTestCase):
         mock_fn = mock.Mock(side_effect=Exception('wut'))
         mock_get_action_fn.return_value = (mock_fn, [], {})
 
-        self._check_main(expected_return_value=10)
+        self._check_main(expected_return_value=255)
         output = self.output.getvalue()
         self.assertIn('Error:', output)
         # assert the traceback is in the output