CBQE-0: tearDown() in rebalanceXDCR updated, as it was same as it base class

Change-Id: I39df1ace6556e0814f2aa5c6461bdc55d1fd54ad
Reviewed-on: http://review.couchbase.org/36257
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>