CBQE-0: fix timeout error for ddoc_ops_during_indexing

Tried to get stats from nodes that were not in cluster

Change-Id: Ie0d671bb3c4982c62e9e2ac76266e0efe0c3b833
Reviewed-on: http://review.couchbase.org/33025
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>