Producer hide librdkafka failures and silently return None as message on poll

Description
===========
In case an error happened on Kerberos request authentification `librdkafka` will provide some logs which also are not returned into python space and for just `None` returned from message poll without an error indication.

How to reproduce
================
```python
consumer_config = {
'bootstrap.servers': 'kafka-int.epm-eco.projects.example.com:9095}',
'schema.registry.url': 'http://schema-registry-int.epm-eco.projects.example.com:8081',
'group.id': 'epm-ddo.consumer.2',
'auto.offset.reset': 'earliest',
'security.protocol': 'SASL_SSL',
'ssl.ca.location': 'conf/integration/epm-eco-int.ca.crt',
'sasl.mechanisms': 'GSSAPI',
'sasl.kerberos.principal': 'kafkaclient',
'sasl.kerberos.kinit.cmd': 'bash -c "cat conf/integration/paswd | /usr/bin/kinit Pavel_Alexeev@PETERSBURG.EXAMPLE.COM"',
'sasl.kerberos.service.name': 'kafka',
# 'log_level': 7, 'debug': 'all' ## Logs will be ONLY in container output
}

topic = '....cdm.LocationChartNode'

consumer = AvroConsumer(consumer_config)
consumer.subscribe([topic])

message = consumer.poll(5)
print(message)

consumer.close()
```
Printed result `None`, if look into the container, `librdkafka` produce errors like:
```
%3|1628784442.369|SASLREFRESH|rdkafka#consumer-34| [thrd:main]: Kerberos ticket refresh failed: bash -c "cat conf/integration/paswd | /usr/bin/kinit Pavel_Alexeev@PETERSBURG.EXAMPLE.COM": exited with code 1
```

Checklist
=========
Please provide the following information:

- [✔] confluent-kafka-python and librdkafka version (`confluent_kafka.version()` and `confluent_kafka.libversion()`):
('1.7.0', 17235968), ('1.7.0', 17236223)
- [✔] Apache Kafka broker version: 5.3.2 (uncertain)
- [✔] Client configuration: Kerberros (SASL_SSL), see full config above in reproduce section
- [✔] Operating system: Linux. Fedora and Ubuntu checked
- [✔] Provide client logs (with `'debug': '..'` as necessary)
- [✔] Provide broker log excerpts: sems irrelevant andI have no access
- [✔] Critical issue: yes. Silently skip errors behavior do not allow rely on behaviour and understand what is there something go wrong or just end of topic reached