CBQE-928: online upgrade tests

Change-Id: I97f91217bb363bf66e68c330ad2c092fccf6951c
Reviewed-on: http://review.couchbase.org/23563
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>