vlserver: Refactor auditing

Refactor auduting to be more like other uses in the code base.
Auditing is now done in a wrapper.

Change-Id: I491aeda31c223e594e3870573871ae10a541d010
Reviewed-on: http://gerrit.openafs.org/11315
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>