Remove tests for Nova V3 API os-instance-usage-audit-log

Removes the positive and negative tests for the Nova V3 API
extension os-instance-usage-audit-log as the extension will not
be supported in the final Nova V3 API release.

See mailing list thread here:

http://lists.openstack.org/pipermail/openstack-dev/2014-February/026670.html

and the Nova corresponding patch:

https://review.openstack.org/#/c/72197/

Change-Id: Iea00cdbfc32d63f5fa08ac4ed9843739e3ae12ce
Merge "Remove tests for Nova V3 API os-instance-usage-audit-log"