CBQE-1042: add rebalance to connection test

Change-Id: I480cc30390f5c1dd371f67dbe8fcd3f3e6729a31
Reviewed-on: http://review.couchbase.org/24966
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>