CBQE-0: add code to update worker's tesrtunner reppsitory

Change-Id: Iec2d09339e4f481792178f58a11e106bb27f253a
Reviewed-on: http://review.couchbase.org/41670
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>