py3: base64 encoding/decoding returns always bytes don't mix it
    
    Using unicode(bytes) call causes undesired side effect that is inserting
    `b` character to result. This obviously causes issues with binary base64 data
    
    https://fedorahosted.org/freeipa/ticket/4985
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>