core: misc kerberos fixups for auth-check

there is no much sense in using kerberos for auth-check, as it has
nothing to do with ldap... a simple kerberos authn extension that
performs kinit should do the trick much better.

but for these who insist... we can provide the service... just a few
fixups.

Change-Id: I8aed9b03abadc05ec3e064ce6bc8e43008fd1e8d
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>