CBQE-2053: check vbuckets suffling during swap rebalance

Change-Id: Ibc6363fd222b2df781af4c61812ae57badafc2bb
Reviewed-on: http://review.couchbase.org/34009
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: buildbot <build@couchbase.com>