vlserver: limit use of regex to admins always

vlserver: limit use of regex to admins always

allow regexes only if the querying user is a superuser.
if the superuser uses up all the resources, well, they could just do
whatever damage directly anyway. means even in unrestricted mode
we are not vulnerable

Change-Id: Ib35d649f31e752ba5ae8373a06b67ea76f97425c
Reviewed-on: http://gerrit.openafs.org/11968
Reviewed-by: Daria Brashear <shadow@your-file-system.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>