CBQE-0:: Improve loading speed of data for rebalance and failover tests

Change-Id: I3f1629d4240637a57817d9a8abba66c603491346
Reviewed-on: http://review.couchbase.org/41271
Reviewed-by: Thuan Nguyen <soccon@gmail.com>
Tested-by: buildbot <build@couchbase.com>