Changing cert-find to do not use only primary key to search in LDAP.
    
    In service.py the primary key is krbCanonicalName, which we
    don't want to use to do searchs. Now, cert-find uses primary
    key or a specified attribute to do searches in LDAP, instead
    of using only a primary key.
    
    https://pagure.io/freeipa/issue/6948
    
    Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>
    Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>