CBQE:0 url to get vb checkpoint changed in recent builds, using ns_server_testrunner_api for the same

Change-Id: I2575240061a516f7863870f3fba8c8bb0bc572a3
Reviewed-on: http://review.couchbase.org/39702
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Aruna Piravi <aruna@couchbase.com>