Add unit test for account/auditor.py

* Here lack tests for a long time; let's add tests for it.
* use mock module instead of monkeypatch in both account/test_auditor.py
  and container/test_auditor.py

Change-Id: I9ea23dc5034f7147629db59b1ef6cb491de9049f
Merge "Add unit test for account/auditor.py"