Fix Build Timestamp Computation and Comparison

KV stats has first vbucket with vb_0 rather than vb_1.
Also fixed the comparison to not ignore 0 seqno. Earlier the
timestamp used to be a fixed size array of 1024 but now its
init with correct number of vbuckets.

Change-Id: Ic7a065096b265ca3bb98c3306e5563cba17442ea