Comment 2 for bug 1836212

The above error was addressed in change I09230fc47b0950aa5a3db839a070613c9c817576 . However, the above error was generated by a nova compute containing this patch, suggesting the fix was incomplete.

The fix does contain a race which could still result in the above error being raised, though: in _do_wait_and_retry_detach get_device_conf_func() might return the present device, which is then deleted before the subsequent call to detachDeviceFlags. I've written a failing unit test to demonstrate this.