CBQE-1003: online xdcr upgrade tests

Change-Id: I395e27b7a00abf837b22dc9ac040d4a530287553
Reviewed-on: http://review.couchbase.org/24577
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>