usr.sbin/praudit: Fix tests after 5619d49e07

Commit 5619d49e07 made the getgrgid() call inside bsm work as
intended so we now print "wheel" instead of a numeric 0 in the rgid field.

Reviewed By: markj
Differential Revision: https://reviews.freebsd.org/D28462

(cherry picked from commit 7791ecf04b48a0c365b003447f479ec890115dfc)