Trove tox tests now generate an error about some mongodb config_file

[Amrith Kumar]

My tox runs are now littered with errors that look like

Traceback (most recent call last):
  File "/opt/stack/trove/trove/tests/unittests/guestagent/test_backups.py", line 534, in test_backup_success
    with self.backup_runner(12345):
  File "trove/guestagent/strategies/backup/experimental/mongo_impl.py", line 46, in __init__
    self.app = mongo_service.MongoDBApp()
  File "trove/guestagent/datastore/experimental/mongodb/service.py", line 74, in __init__
    revision_dir = self._init_overrides_dir()
  File "trove/guestagent/datastore/experimental/mongodb/service.py", line 60, in _init_overrides_dir
    os.path.dirname(CONFIG_FILE),
  File "/opt/stack/trove/.tox/py27/lib/python2.7/posixpath.py", line 129, in dirname
    i = p.rfind('/') + 1
AttributeError: 'NoneType' object has no attribute 'rfind'

I have a change for this, will push it up

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/223224

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/223224
Committed: https://git.openstack.org/cgit/openstack/trove/commit/?id=c1cecebdf654cf0e36c8c75ca0c3dbfdfb66e869
Submitter: Jenkins
Branch: master

commit c1cecebdf654cf0e36c8c75ca0c3dbfdfb66e869
Author: Amrith Kumar <email address hidden>
Date: Mon Sep 14 16:56:09 2015 +0000

    Properly patch _init_overrides_dir in MongoDB

    Since most of us don't have MongoDB installed on our
    desktop/development environment, tox tests will fail because some
    config paths for Mongo aren't available.

    The change proposed here is merely to mock the _init_overrides_dir
    properly in changes that would otherwise stub their toes on this.

    It is my understanding that this issue was introduced in Change-Id:
    Iaca9cc9e3ce1e6521839062fc9458c1b987f9464 which sought to address bug
    1485158.

    The reason this problem occurs on my machine (and likely on other
    developers workstation) is that I don't have MongoDB installed. The
    reason this doesn't impact the gate is that those machines have
    MongoDB installed (for ceiliometer).

    Change-Id: I0f3d24b95a7d2ef1e23a0f1fd8f60bc496261f70
    Closes-Bug: #1495573