ldif: handle attribute names as strings
    
    ldif.LDIFRecordList handles all attribute names as utf-8 strings
    and all attribute values as bytes. If we take the attribute value
    and try to search for it in the entry (= dictionary), if it contains
    the attribute name as a key (which is a string), their hashes match.
    However, even if hashes match, Python needs to make sure those two
    are the same in case of a hash collision, so it tries to compare them.
    This causes BytesWarning exception when running in strict mode
    because `bytes` and `str` instances cannot be compared. KeyError
    would be thrown in a non-strict mode.
    
    Also, when later passing the attr to replace_value(), we need for it
    to be `str` otherwise the modifications handler fails because it
    tries to sort the attributes it's modifying but that's a bit less
    poetic issue than the first one.
    
    https://pagure.io/freeipa/issue/7129
    
    Reviewed-By: Michal Reznik <mreznik@redhat.com>