Adds missing expected_errors for V3 API multinic extension

The V3 API multinic extension is missing the expected errors
decorators which means that unexpected internal Nova exceptions
are not caught correctly. This patch adds the expected error
decorators.

Change-Id: I99311275197bb5123079c8910855386252028dec
Closes-Bug: 1303781
Remove mention of nova-manage.conf from nova-manage.rst

As of commit 07ee9639 three years ago nova-manage.conf is no longer
used, so let's clean up the man page.

Closes-Bug: #1304580

Change-Id: Ie061733da4bd0337f510e17b6dd7ca5bae14b7de
Merge "Adds missing expected_errors for V3 API multinic extension"
Merge "Remove mention of nova-manage.conf from nova-manage.rst"