Lower logging level on replica not available and commit

[ecanzonieri]

These two log prints are very noisy when we deal with high volume topics and large clusters, and in my opinion not particularly useful from a client perspective unless in debug level.
The replica not available log, indeed, is not specific of the topic/partition of the particular consumer/producer. In a Kafka cluster with a lots of topics this ends up flooding the logs with warning about under replicated topics which the user most of the times is not interested in. This is a very important information for the cluster administrator, but the latter should rely on metrics and logging provided by Kafka itself instead of a client library.