MB-25097: In DCP consumer, improve handling of message processed response
MB-25097: In DCP consumer, improve handling of message processed response

A DCP consumer handles the response of the passive stream processing
an item. This is a refactor commit which improves that handling.

Change-Id: I462ecb8757ec103284e628f9adcff28452412088
Reviewed-on: http://review.couchbase.org/80285
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine