ipatests: fix expected output for ipahealthcheck.ipa.host
    
    ipa-healthcheck commit e69589d5 changed the output when a service
    keytab is missing to not report the GSSAPI error but to report
    that the keytab doesn't exist at all. This distinguishes from real
    Kerberos issues like kvno.
    
    Fixes: https://pagure.io/freeipa/issue/9482
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>
    Reviewed-By: Michal Polovka <mpolovka@redhat.com>