Got 'ImportError' when build doc

[Eric Xie]

Description
===========
Got 'ImportError' when i built ironic's documents with command ``tox -edocs``.

Steps to reproduce
==================
* tox -edocs

Expected result
===============
No error prompt.

Actual result
=============
Got 'ImportError'.

Environment
===========
# git log
commit 9842f401874f4010762afb45d4263e109614b193
Merge: 1cb779e 4fa2412
Author: Jenkins <email address hidden>
Date: Wed Jan 4 12:18:27 2017 +0000

    Merge "Create a table to track loaded interfaces"

Logs
===========
/work/ironic-master/doc/source/api/ironic.nova.compute.manager.rst:4: WARNING: autodoc: failed to import module u'ironic.nova.compute.manager'; the following exception was raised:
Traceback (most recent call last):
  File "/work/ironic-master/.tox/venv/lib/python2.7/site-packages/sphinx/ext/autodoc.py", line 386, in import_object
    __import__(self.modname)
  File "/work/ironic-master/ironic/nova/compute/manager.py", line 31, in <module>
    from nova.i18n import _LW
ImportError: No module named i18n

[Dmitry Tantsur (divius)]

Please try rebuilding your environment with adding -r flag to the tox call. I've just rebuilt docs via 'tox -edocs -r' successfully.

[Eric Xie (eric-xie)]

I tried the latest code and found this issue also exist.

commit eae8e07132edf00bc5b51aa8342ad22ab3c2cc60
Author: Jim Rollenhagen <email address hidden>
Date: Fri Jan 20 20:30:09 2017 +0000

    Fix api-ref warnings

    A few missing parameters breaking the build on latest api-ref package,
    fix them.

    Change-Id: I7769844b8a766c78418c28991b97827014886ec4
    Closes-Bug: #1658187

[Eric Xie (eric-xie)]

@dmitry, was the package 'nova' installed in your environment?

I think that the 'nova' package should be included in requirement.txt.

[Ramamani Yeleswarapu (ramamani-yeleswarapu)]

Eric, this error cannot be reproduced; building docs succeeds. I've tested it after this commit: https://github.com/openstack/ironic/commit/4c61f1ac1828859ae5f76cd91c382cfb215bc412

[Eric Xie (eric-xie)]

@Ramamani, i reproduced this issue with the latest code, and fount it has been gone.
So i changed this bug to 'invalid'.