install: introduce generic Kerberos Augeas lens
    
    Introduce new IPAKrb5 lens to handle krb5.conf and kdc.conf changes using
    Augeas. The stock Krb5 lens does not work on our krb5.conf and kdc.conf.
    
    https://pagure.io/freeipa/issue/6831
    
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
    Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>