installer service: fix typo in service entry
    
    The typo would result in incorrect resolution of existing keys and
    their existence wasn't properly logged as intended.
    
    Related https://pagure.io/freeipa/issue/6920
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>
    Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>