The MIT krb5 kadmin protocol originally used kadmin/admin as the
service principal. Commits 493f0da5fbf92b0ac2f10e887706d1964d8a15e8
and 5cfaec38a8e8f1c4b76228ba0a252987af797ca4 changed it to use
kadmin/hostname preferentially, with kadmin/admin as a fallback, for
interoperability with the Solaris SEAM administrative protocol.
Change the preference order so that kadmin/admin is tried first, with
kadmin/hostname as a fallback.