Use correct default principal for kadmin -n

Use WELLKNOWN/ANONYMOUS@realm as the default principal for kadmin -n,
just like we do for kinit -n.

https://github.com/krb5/krb5/commit/a30a82abc72c2a1a8d25948fe9cd1af49eaf62ec
Author: Greg Hudson <ghudson@mit.edu>
Commit: a30a82abc72c2a1a8d25948fe9cd1af49eaf62ec
Branch: master
 src/kadmin/cli/kadmin.c |   20 ++++++++++++++------
 1 files changed, 14 insertions(+), 6 deletions(-)