MB-11928: Fast path for rollback to 0

Right now we run through all of the headers even if we have to
rollback to 0. This change provides a fast path to rollback to
zero by immediately resetting the vbucket.

Change-Id: I8e7b62ec711838894c4eda92eaff78704bd94d50
Reviewed-on: http://review.couchbase.org/40595
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>