Re-added the offset fetch request in consumer and added logging

Re-added the offset fetch request in consumer, added logging around a problematic struct.pack in protocol.py to help us nail down an issue.

(the fetch request stuff was commented out so I could pull into mumrah/kafka-python, I am now correcting this for the "official" Has-Offers version)

The changes to protocol.py are already live on USW05 as part of debugging the issue there.