MB-7518: Fix snapshotVbuckets logic that was broken by prev change

Change-Id: Ie6b26b4454d2edb301af8bf4a3bb9124d2dfa1ba
Reviewed-on: http://review.couchbase.org/26052
Reviewed-by: Jin Lim <jin@couchbase.com>
Tested-by: abhinav dangeti <abhinav.dangeti@gmail.com>