CBQE-1406: fix online_swap_upgrade test

Change-Id: I220215c574484b5049f233a13cdd93df0ee95a04
Reviewed-on: http://review.couchbase.org/27128
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Deepkaran Salooja <deepkaran.salooja@globallogic.com>