CBQE-0: high_seqno is now abs_highseq_no

DCP v-bucket stat change

Change in vbucket-seqno stat

The stat high_seqno will be abs_high_seqno

high_seqno now finds by how much replica v-bucket is trailing behind active v-bucket.  Used for replication purpose.

This change was as a result of the following bug:: https://www.couchbase.com/issues/browse/MB-11299

Change-Id: Ica0d60aa62a6671167608ca43262d5586d90e94b
Reviewed-on: http://review.couchbase.org/40655
Reviewed-by: Thuan Nguyen <soccon@gmail.com>
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>