replication: fix regression in get_agreement_type
    
    dcb6916a3b0601e33b08e12aeb25357efed6812b introduced a regression where
    get_agreement_type does not raise NotFound error if an agreement for host
    does not exist. The exception was swallowed by get_replication_agreement.
    
    Reviewed-By: Tomas Babej <tbabej@redhat.com>