MB-11379: Optimize way to calculate max seqno

Instead of browsing throw data file to get max seqno for each vbucket,
we can persist this info as part of meta file for each data file.
In this way, we can avoid multiple full table scanning which becomes
too time consuming when data set size is large.

Change-Id: I42f1b23a2dd280eb611867a1be520dd874784c30
Reviewed-on: http://review.couchbase.org/38215
Reviewed-by: Steve Yen <steve.yen@gmail.com>
Tested-by: Bin Cui <bin.cui@gmail.com>