log error when ReadEntryProcessor IOException

[AnonHxy]

Descriptions of the changes in this PR:

Motivation

Change the log-level to error when ReadEntryProcessor throw IOException. The reason is that:

1. IOException should not happen frequently，so the error log will not print too much
2. It will be convenient for troubleshooting if we print the error log.
3. Also we can see that ReadEntryProcessorV3 has printed the error log

https://github.com/apache/bookkeeper/blob/dc2bb1dfed38d7f9ad7a29fc92bd907e51af5b21/bookkeeper-server/src/main/java/org/apache/bookkeeper/proto/ReadEntryProcessorV3.java#L233-L236

Changes

log.debug -> log.error