MB-11459: Add logging to diagnose incorrect high seqno on warmup

Change-Id: Id82d7c7569e37143a0413a90b54331452c8b2502
Reviewed-on: http://review.couchbase.org/38816
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>