nagios_client: Fix the check_ipa_replication plugin
    
    It looks like the data it retrieves is in bytes and thus needs to be
    decoded into a unicode string so we can use it as a regular string
    in our code later.
    
    Fixes https://pagure.io/fedora-infrastructure/issue/9372
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>